Kemi Badenoch demanded that Keir Starmer apologises to Donald Trump for jibes by Labour figures today.
The new Tory leader slammed Sir Keir, Foreign Secretary David Lammy and other senior figures for their comments about the president elect in her debut at PMQs.
She insisted that Sir Keir must invite Mr Trump to visit the UK and address both Houses of Parliament.
The attack came after the premier opened the exchanges by congratulating the Republican. Having had dinner with president-elect Trump just a few weeks ago I look forward to working with him in the years to come, he said.
But Ms Badenoch pointed to remarks such as Mr Lammy describing the resurgent politician as a Neo-Nazi sympathiser.
She asked whether they had said sorry to Mr Trump over dinner in New York - saying that he should be doing so.
Sir Keir is facing a major headache with Mr Trumps stunning US election win, after tensions flared over Labour supporters helping to campaign for the Democrat contender.
The PM has also repeatedly clashed with billionaire Elon Musk, who looks certain to end up playing a key role in the Trump administration.
When Mr Trump was last president Labour MPs including Mr Lammy signed an early day motion arguing he should not be allowed the honour of addressing both Houses of Parliament during a state visit.
Kemi Badenoch is making her debut at PMQs today as Keir Starmer struggles with Budget backlash and the US election fallout
The attack came after the premier opened the exchanges by congratulating the Republican
The PM has also repeatedly clashed with billionaire Elon Musk , who could end up playing a key role in a Trump (pictured) administration should the Republic emerge victorious
Government sources have been playing up the private dinner Sir Keir and Mr Lammy had with Mr Trump in New York in September, insisting they had struck up a good relationship.
But during the bitter campaign Mr Trumps team filed an official complaint with federal election authorities accusing Labour of making illegal foreign national contributions.
Around 100 activists travelled to swing states to canvass for the Harris ticket - although Labour insisted they went at their own expense.
There was also anger that senior figures from the party went to the Democratic National Convention in August and met Harris aides. The two parties have long-term ties.
In interviews at the Commonwealth summit in Samoa last month, Sir Keir tried to gloss over fears the spat could derail the Special Relationship if Mr Trump wins.
He insisted that the situation needed to be put in perspective as volunteers from parties have gone to help out in every previous election.
As a backbench MP in 2018, Mr Lammy wrote in Time magazine: Trump is not only a woman-hating, neo-Nazi-sympathising sociopath.
He is also a profound threat to the international order that has been the foundation of Western progress for so long.
The clashes come after Ms Badenoch put the finishing touches to her shadow cabinet yesterday, drafting in figures from all wings of the party.
She has given Mel Stride the key Treasury brief and unveiled a stunning comeback for Priti Patel - who will be in charge of foreign affairs.
Meanwhile, defeated rival Robert Jenrick has agreed to become shadow justice secretary, and Chris Philp covering the Home Office.
Close ally Laura Trott has responsibility for education, and Andrew Griffith the business portfolio.
But there was nothing for another former leadership contender, Tom Tugendhat - who is understood to have said he did not want to be on the front bench. He joins James Cleverly, another contender, on the backbenches.
The government has been embroiled in a row over announcing that agricultural assets worth more than £1million will no longer be exempt from inheritance tax, which Opposition MPs have been calling on ministers to reverse.
From April 2026, a tax of 20 per cent will be raised on the value of inherited farming assets above the threshold.
While this still represents a tax relief compared to the standard rate, the move has sparked fury from farming unions who say it will destroy family farms and make the UK more reliant on imports.
Labour has also faced anger for imposing a massive national insurance increase after claiming during the election campaign that they had no intention of doing so.
Sir Keir insists he has stuck by a promise not to increase the burden on working people.
The full shadow cabinet line-up met yesterday morning, with Ms Badenoch underlining her determination to fix rifts in the party.
She said the process of renewing our great party has now begun. I am delighted to have appointed my Shadow Cabinet, which draws on the talents of people from across the Conservative Party, based on meritocracy and with a breadth of experience and perspective, just as I promised during the campaign, she said.
Ms Badenoch said: Our partys problems will only be solved with a team effort, and I am confident my Shadow Cabinet ministers will deliver effective opposition as we seek to win back the trust of the public.
We will now get to work holding Labour to account and rebuilding our party based on Conservative principles and values.
The process of renewing our great party has now begun.
However, Ms Badenochs task has been made more difficult by having a paltry 121 Tory MPs to draw on - and big beasts such as James Cleverly and Jeremy Hunt announcing that they would not serve.
Veteran Mark Francois, a supporter of Mr Jenrick during the campaign, has been appointed as shadow defence minister.
Gagan Mohindra, who endorsed Mr Cleverly, becomes Deputy Chief Whip.
Kieran Mullan, who backed Ms Badenoch, is the new shadow justice minister.
Yesterday Ms Badenoch told Tory staffers that she believed the party could recover from the election drubbing in July in time to take on and beat Labour at the next election.
She told them we can turn this around in one term, a source said.
The new leader told staff to focus on next Mays local council elections as the first target on the road to recovery.
A source said both Ms Patel and Mr Stride are experienced MPs who stood in the leadership contest and represent different wings of the Conservative Party.
The source argued that the appointments demonstrated Kemis desire to unite.
Victoria Atkins is understood to have requested a move from the health portfolio to environment because she wants to take the fight to Labour on their treatment of farmers.
A friend of Ms Patel told MailOnline she was a great appointment. Theyve been chatting a fair bit and see eye-to-eye on a lot, they said.
Rebecca Harris has been made chief whip, while Nigel Huddleston and Lord Dominic Johnson are joint party chairs.
During the campaign Mr Jenrick criticised Ms Badenoch for a lack of policy.
Yesterday, she told staff that new policy positions would begin to emerge soon but said it was right to start with principles and the things that bind us as Conservatives together: freedom of speech, freedom of association, free enterprise, personal responsibility – what distinguishes us from all the parties of the Left who think more government is the answer to everything.
She urged staff to think again about the way the party approaches politics after its worst defeat in history.
She told them they dont have to do things the way theyve always been done, a source said.
Its time to try something different. She told them to let their creative juices flow.
Tory insiders said Mr Jenrick had accepted the justice job after tense negotiations over exactly what role he should play.
An ally said: Rob thinks the party needs to come together and take the fight to Labour. Unity could not be more important. Hes eager to expose Labours dreadful record on law and order.
The role will involve him discussing the impact of the European Convention on Human Rights, where he and the new leader had differing views during the election campaign.
She beat Mr Jenrick on Saturday by 53,806 votes to 41,388.
Kemi Badenoch gathered her shadow cabinet for the first time today as she moves to unite the Tories
The new leader has given Mel Stride the key Treasury brief and signalled a stunning comeback for Priti Patel - who will be covering foreign affairs
James Cleverly has ruled out serving on the new leaders front bench