President Donald Trump has waded into Britain’s election campaign, lavishing praise on Prime Minister Boris Johnson and savaging the main rival facing Johnson in his Dec. 12 snap election, Labour Party leader Jeremy Corbyn. But we're not so sure Trump's comments did his “friend” any favors.

In a wide-ranging interview Thursday with Brexit Party leader Nigel Farage, a friend of the U.S. president, Trump slammed Johnson’s proposed Brexit deal with the European Union, saying it would mean the U.S. wouldn’t be able to negotiate a trade deal with Britain.

“To be honest with you, this deal, under certain aspects of the deal, you can’t do it. You can’t trade. We can’t make a trade deal with the U.K.,” he told Farage in the interview for broadcaster LBC.

“I think we can do many times the numbers we’re doing right now, and certainly much bigger numbers than you’re doing under the EU.”

His comments, which directly contradicted Johnson’s pledge to negotiate a free trade agreement with the U.S. after leaving the EU, prompted Downing Street to issue a rebuttal Friday.

“The PM negotiated a new deal which ensures that we take back control of our laws, trade, borders and money – a deal which people said he could never negotiate,” said the statement. “Under this new deal, the whole of the U.K. will leave the EU Customs Union, which means we can strike our own free trade deals.”

In further comments that likely had Johnson’s campaign team wincing, Trump — who is hugely unpopular in the UK — described the UK prime minister as a “fantastic man” and said they had “a great friendship.”

“When he was running, they were saying, 'He’s the Trump, he’s the Trump.' We have a lot of the same things going,” he said. He also urged Johnson and Farage to team up and form an “unstoppable force” to win the election.

Analysts predict Farage’s Brexit Party will draw some voters away from Johnson’s Conservatives in the December election, potentially costing the Tories vital seats unless they can reach a deal with Farage not to contest marginal electorates. Farage said Friday that he wanted to form a “Leave alliance” with the Conservatives but that it would require Johnson to tear up the EU withdrawal agreement he reached with the EU, which Farage said was “not Brexit.”

If Johnson didn’t agree to a pact, Farage said his party would run candidates in every seat in England, Scotland, and Wales.

Trump also had scathing criticism for Labour leader Jeremy Corbyn, telling Farage the veteran socialist would be “so bad for your country” and “take you into such bad places.”

Corbyn immediately seized on Trump’s comments to highlight the ties between Johnson and Trump — and to fuel voter fears that any U.S. trade deal could see a mass selloff of public services to American corporations, including the treasured National Health Service.

“Donald Trump is trying to interfere in Britain’s election to get his friend Boris Johnson elected,” he tweeted.

“It was Trump who said in June the NHS is ‘on the table’. And he knows if Labour wins, U.S. corporations won’t get their hands on it. Our NHS is not for sale.”

It’s not the first time Trump has weighed in on Britain’s leadership or other sensitive issues. In July last year, former Prime Minister Theresa May’s Brexit strategy took a hit when Trump said her proposed agreement with the EU would probably “kill” the chances of a U.S. trade deal.

And during the race to become May’s successor earlier this year, he unambiguously backed Johnson, saying he'd make a great leader because he was seen as “Britain’s Trump.” That’s not quite the compliment he thinks it is: Polling shows two-thirds of British people have a negative view of the U.S. leader.