First, in a box office committee hearing, his claims that he followed "due process" in appointing Peter Mandelson as US ambassador could face serious challenges.
And second, in an emergency Commons debate secured by Kemi Badenoch, the PM faces demands for a potentially career-ending probe into claims that he misled MPs.
Judgement Day: Part One
The day of drama at Westminster begins with a 9am appearance at the foreign affairs select committee by former top Foreign Office mandarin Sir Philip Barton.
His evidence to the committee's inquiry into the Mandelson vetting scandal is potentially hugely damaging because he was strongly opposed to Mandelson's appointment.
Last week his successor, Sir Olly Robbins, told the committee the Foreign Office was put under "constant pressure" by 10 Downing Street to give the disgraced peer the job before vetting.
And in a new blow to the PM, Foreign Office security chief Ian Collard backed Sir Olly's claim about pressure from Downing Street due to "regular contact from No 10", he claimed.
In written evidence to the committee after he was blocked from appearing in person, Mr Collard said he felt "pressure to deliver a rapid outcome" during the vetting of Mandelson.
Judgement Day: Part Two
Next up, at 11am, is Sir Keir's controversial former chief of staff Morgan McSweeney. The committee has heard he told Sir Phillip to "just f***king approve it", a claim he denies.
Mr McSweeney is also expected to be quizzed on the theft last October of his mobile phone, containing vital records, something the Tories say is "fishy" and "beggars belief".
Then in the Commons, MPs will debate and vote on a motion tabled by the Tory leader demanding an inquiry into the PM by the powerful Privileges Committee of MPs.
It was this committee which in 2022 produced a damning report concluding that Boris Johnson lied to MPs over "partygate", which brought about his downfall as PM.
Starmer stands firm
Ahead of his judgement day in the Commons, Sir Keir came out fighting in a defiant interview with Cathy Newman on Sky News and later in a tough speech to Labour MPs.
Asked by Cathy Newman why he didn't just let the Privileges Committee investigate and be proven right, he replied: "Because it's a stunt. We've got huge amounts of transparency going on already."
And in his speech to a packed meeting of the Parliamentary Labour Party, he described the allegations put forward by the Conservatives as "totally baseless" and "absolutely ridiculous".
"This is a political stunt by our opponents who want to bring us down, obscure our message, and stop us getting on with our work," the PM told Labour MPs.
"And the timing tells you everything nine days before local elections. Tomorrow is pure politics, and we need to stand together against it."
But will he win the vote?
After the meeting, Chief Whip Jonathan Reynolds confirmed to Sky News that Labour MPs would be on a three-line whip to vote against the Tory motion. "We'll vote it down," he said.
With its huge Commons majority, the government should comfortably win the vote, because even those Labour MPs who want Sir Keir to quit don't want to hand a victory to the Tories.
And even malcontents and supporters of Angela Rayner and Andy Burnham accept that now, nine days before vital elections, is not the time to fire the starting gun on a leadership race.
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Ahead of the vote, Labour grandees including Gordon Brown urged MPs to back Sir Keir. The former PM told Labour MPs to "put the country first" when there are "conflicts raging around the world".
Downing Street also published a letter from ex-civil service chief Sir Chris Wormald to Sir Keir, declaring "the appropriate processes were followed in both the appointment and withdrawal" of Mandelson.
But Kemi Badenoch responded on X: "Rubbish. The only advice that matters is the advice Starmer was given BEFORE appointing Mandelson. Not the hasty justification written a year later."
It's the first state visit to the US by a British monarch since 2007, when Queen Elizabeth II met with George W Bush.
The trip got under way on Monday when King Charles and Queen Camilla stepped out from their plane at Joint Base Andrews and walked down the stairs to a red carpet before shaking hands with officials waiting to greet them.
As it happened: How King's first day in US unfolded
Charles and Camilla were both then gifted with a bouquet before departing the airfield in a car. They also stopped to listen to a military band playing the national anthems of the UK and the US.
Next up, for the royals' first official appointment, was a meeting with Donald Trump and Melania Trump at the White House.
They were welcomed on the South Lawn by the president and first lady, with the two couples shaking hands and embracing each other.
The royals then posed for photos before heading inside the US president's residence, while Charles and Trump could be seen having extended conversations.
Before their arrival, it was agreed that the King would meet with Mr Trump behind closed doors.
We have no details on what they discussed, but we do have pictures of the Trumps showing the royals around the White House – and having tea.
The King and Queen also attended a garden party at the British embassy in Washington.
Sky's royal correspondent Laura Bundock noted during the trip that it was a "gentle start", adding: "He has never been hosted by a president like Donald Trump.
"We know Trump loves the Royal Family, but we also know that Trump can't keep quiet at times. He is an unpredictable president."
What's next on the agenda?
While we don't know the exact timings, the King is set to address Congress today, which Buckingham Palace said is expected to last for around 20 minutes.
It will be only the second time a British monarch has addressed the US Congress, after Queen Elizabeth II in 1991.
Charles will reflect on how "time and again, our two countries have always found ways to come together" and how defence, intelligence and security ties "are measured not in years but in decades", a palace spokesperson said.
He's expected to describe UK-US ties as "one of the greatest alliances in human history".
Next up, the King and Queen will also attend a state dinner at the White House and will travel to New York to commemorate the 25th anniversary of the September 11 terrorist attacks.
They will also mark 250 years of US independence at a "block party" in Virginia, and – on a much lighter occasion – the Queen will give a specially made toy of the Winnie the Pooh character Roo to the New York Public Library to complete a set of the beloved characters in one of the institution's collections.
Olivia Bailey told the Commons "some form of age or functionality restriction" will be brought in after the House of Lords backed an outright ban for the fourth time.
MPs have already overturned the Lords' proposed social media ban three times, saying a government consultation on the matter needs to conclude first.
Speaking to the Commons after the latest vote, Ms Bailey said ministers had "listened carefully to the concerns raised across both Houses about the importance of the government acting swiftly once the consultation has concluded".
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She added: "The government has said repeatedly that it is a question of how we act, not if, but to put it beyond any doubt, we are playing a clear statutory requirement that the secretary of state must, rather than may, act following the consultation.
"This brings forward regulations without pre-empting the consultation's outcomes and does not ignore the tens of thousands of parents and children who have already engaged with us."
The education minister then said that "the status quo cannot continue" and added: "We are clear that under any outcome, we will impose some form of age or functionality restrictions for children under 16.
"I can also confirm that consideration of restrictions such as curfews will be in addition, not instead of this."
'Huge step forward'
The House of Lords voted 316 to 165 in favour of Conservative former minister Lord Nash's amendment to the Children's Wellbeing and Schools Bill, which would outright ban social media for those under 16 years old.
Shadow education secretary Laura Trott said the vote had helped secure a "commitment" from the government to introduce an age restriction, describing it as a "huge step forward in keeping children safe".
The Conservatives have been calling for a ban for months. It would see the UK follow in the footsteps of Australia, while other countries in Europe – including France and Spain – consider similar restrictions.
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Speaking before Monday's developments in parliament, a cabinet minister told Sky News a decision on a ban would come before the end of the year.
Environment Secretary says Emma Reynolds said ministers will "act relatively quickly" once the government's consultation concludes in a few weeks.
It's among 150 suspected cases where abuse victims ended their lives in the year ending March 2025, as part of the annual Crime Survey for England and Wales.
The report also shows a higher proportion of young people aged 16 to 19 were victims of domestic abuse, at 18.2%, compared to those aged 25 and older.
The national policing lead for domestic abuse, assistant commissioner Louisa Rolfe, said access to violent pornography and "toxic influencers" online may be fuelling abuse cases among teenagers.
"People are now much more likely to access violent pornography, which normalises violence and behaviour in a relationship," she said, highlighting "hugely dangerous" non-fatal strangulation.
She added: "We see the connection between the sort of sense of toxic influencers online and their sort of views that are promoted about women and women's status in society."
The report shows a higher proportion of police-recorded domestic homicides where a victim committed suicide after suffering abuse, compared to those where a partner killed the victim.
In the five years of the annual Domestic Homicide Project, which analyses police-recorded domestic homicides, 553 were suicides following domestic abuse.
Four of them were where the victim was under 16 and the perpetrator was over 18 – three were adult family members and one an intimate partner.
Jess Phillips, the minister for safeguarding and violence against women and girls, said the report "reinforces the need for tougher action to stop perpetrators causing harm".
"Our Violence Against Women and Girls Strategy sets out how we are rooting out the causes of domestic abuse-related deaths and deploying the full power of the state to crack down on these vile crimes," she added.
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More domestic abuse victims die by suicide than homicide
'Separate suicide from domestic abuse'
The report comes as campaigners push for a new law to make suicide for domestic abuse a specific criminal offence separate from manslaughter to make it easier for juries to understand.
"I'm speculating that the average juror sees manslaughter as maybe a punch-up in a car park, other types of killing," said Frank Mullane, the CEO of support service Advocacy After Fatal Domestic Abuse.
"I think if we separate suicide from domestic abuse, it will help educate the public."
In the past five years, there have been 17 cases where domestic abuse charges have been brought after a victim committed suicide, three of which investigated possible manslaughter.
Seven more posthumous cases are also expected, and the number of these investigations is expected to rise.
Over the past five years, there were 1,452 reported deaths linked to domestic abuse.
In the year to March 2025, 347 deaths were reported, an increase of 85 on the previous year, most of which are suspected suicides.
Police believe the increase is down to increased recording of these cases rather than a rise in the number of crimes being committed.
Anyone feeling emotionally distressed or suicidal can call Samaritans for free on 116 123 or visit samaritans.org in the UK. In the US, call the Samaritans branch in your area or 1 (800) 273-TALK.
If you suspect you are being abused and need to speak to someone, there are people who can help you.
The National Domestic Violence Helpline: 0808 2000 247
Respect, the helpline for male domestic abuse victims: 0808 8010327
Galop, the LGBT+ anti-violence charity: 0800 999 5428
Just days before the shooting at the White House Correspondents Association (WHCA) dinner in Washington, Kimmel did the sketch about the event on his programme Jimmy Kimmel Live!.
He joked Mrs Trump had a "glow like an expectant widow".
There was no indication Kimmel was referring to violence in the sketch.
Reacting on Truth Social, the US president said Disney and ABC should immediately sack the comedian, who was briefly taken off-air last year over comments about the killing of Trump supporter Charlie Kirk.
Mr Trump wrote: "I appreciate that so many people are incensed by Kimmel's despicable call to violence, and normally would not be responsive to anything that he said, but this is something far beyond the pale."
The first lady reiterated her husband's post on X, where she said Kimmel's "hateful and violent rhetoric" intends to divide the US.
"His monologue about my family isn't comedy - his words are corrosive and deepen the political sickness within America.
"People like Kimmel shouldn't have the opportunity to enter our homes each evening to spread hate.
"A coward, Kimmel hides behind ABC because he knows the network will keep running cover to protect him.
"Enough is enough. It is time for ABC to take a stand. How many times will ABC's leadership enable Kimmel's atrocious behaviour at the expense of our community."
What did the sketch actually show?
The sketch depicted Kimmel in a tuxedo, standing behind a podium pretending to deliver a comic routine for the WHCA dinner with "cutaways" to the Trumps.
"Our first lady, Melania, is here. So beautiful. Mrs Trump, you have a glow like an expectant widow," he joked.
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Kimmel has long targeted Trump in his comedy and is no fan of the president. He came close to tears following the Republican's 2024 election win, describing it as a "terrible night".
His suspension for comments about the assassination of right-wing influencer Kirk in September was met with criticism towards the administration for infringing on freedom of speech, leading to Kimmel's reinstatement five days later.
On his return, Kimmel said it was "never my intention to make light of" Kirk's death, adding that he didn't think there was anything funny about it.