Donald Trump is pushing away one of his few close allies, French President Emmanuel Macron, as experts warn of an emerging European power vacuum and some GOP lawmakers defend the U.S. president’s latest brash move.

The two presidents have little in common but quickly became unlikely allies. Trump is a businessman and former reality television star. Macron was a philosophy major who became a finance and economic wonk. A bromance developed, and Trump feted Macron during an official visit that included a private dinner at George Washington’s Mount Vernon estate and an elegant state dinner at the White House.

But seven months later, the two are on a path toward a trans-Atlantic breakup.

Many U.S. lawmakers — Republicans and Democrats — have warned Trump to avoid alienating longtime close allies. And they want him to end a nasty trade flap with the EU, which many experts see Macron leading as German Chancellor Angela Merkel soon will exit the global stage.

Should the Trump-Macron relationship continue to deteriorate, it will only add to the global issues facing the House Foreign Affairs and Senate Foreign Relations committees — as well as those that oversee U.S. intelligence and defense matters. As the House prepares to flip to Democratic control, those committees are prepping more aggressive oversight of the Trump presidency, including its foreign policy.

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And in a new twist delivered via a Tuesday morning tweet, Trump appears to be defending Russian President Vladimir Putin instead of Macron — even as House Democrats are poised to rekindle that chamber’s investigation of Russia’s 2016 election meddling and possible coordination with Trump’s campaign.

Incoming House Judiciary Chairman Jerrold Nadler of New York says once he takes the gavel, the panel will look into Russia’s 2016 meddling efforts, including hearings that, in part, will seek to determine whether Russians worked with members of the president’s inner circle.

“We’ll clearly look into [Russian interference],” Nadler said.

Trump’s siding with Putin on Tuesday over the French leader came as some Republican lawmakers continue to defend the president’s actions toward traditional U.S. allies.

Trump seems agitated by a speech Macron gave during 1918 Armistice festivities in France on Sunday, during which he took a clear shot at Trump’s self-description as a “nationalist.” The French leader called nationalism a “betrayal of patriotism.”

Asked Sunday if he is concerned that Trump’s “nationalist” philosophy and actions toward American allies are threatening the post-World War II order, Senate Armed Services member Lindsey Graham responded: “Oh, no.”

“I think he’s got a political problem at home, Macron does, and probably picking a fight with Trump is good politics,” Graham, a Trump critic-turned-confidant, told CBS Sunday. “I like the idea of President Trump pushing NATO to pay more. … I think the main friction is getting out of the Iran deal, which I thought was bad for America and really bad for the world. So, Republican presidents always have a hard time in Europe. I’m not really worried about this at all.”

Trump hit the same note Tuesday, suggesting Macron’s struggles with his own countrymen led Macron last week to suggest European countries should depend less on the United States to defend them against Russia.

The remark triggered a critical Trump tweet as Air Force One was about to land in Paris on Friday, followed by less-than-warm body language between Trump and Macron all weekend. The tensions continued Tuesday, when Trump suggested Macron is wrong to view Putin and his military as a threat.

“Emmanuel Macron suggests building its own army to protect Europe against the U.S., China and Russia,” Trump wrote. “But it was Germany in World Wars One & Two — How did that work out for France? They were starting to learn German in Paris before the U.S. came along.”

President Macron of France has just suggested that Europe build its own military in order to protect itself from the U.S., China and Russia. Very insulting, but perhaps Europe should first pay its fair share of NATO, which the U.S. subsidizes greatly!

— Donald J. Trump (@realDonaldTrump) November 9, 2018

The unique and aggressive messaging of this presidency continued with that tweet. U.S. presidents of both parties have described defeating Adolf Hitler’s Germany as something America and Europeans — and Russia — did together rather than something America did mostly on its own. The rhetoric is part of the reason Trump received a muted response from many European leaders on the weekend trip.

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“The problem is that Emmanuel suffers from a very low Approval Rating in France, 26%, and an unemployment rate of almost 10%,” Trump wrote, adding of Macron’s call for a European military: “He was just trying to get onto another subject.”

The problem is that Emmanuel suffers from a very low Approval Rating in France, 26%, and an unemployment rate of almost 10%. He was just trying to get onto another subject. By the way, there is no country more Nationalist than France, very proud people-and rightfully so!……..

— Donald J. Trump (@realDonaldTrump) November 13, 2018

……MAKE FRANCE GREAT AGAIN!

— Donald J. Trump (@realDonaldTrump) November 13, 2018

Some foreign policy analysts say that despite his best efforts, Macron’s initial chumminess toward Trump has failed to make the U.S. president more engaged in Europe. And his more recent tough talk, experts say, has failed to make clear he or any other European leader can replace a disengaged and “nationalist” America.

“The Trump-Macron relationship is based on what I call a ‘compartmentalized cooperation,’ which mirrors both Trump’s transactionalism and Macron’s pragmatism,” said Alexandra de Hoop Scheffer, who heads the German Marshall Fund’s Paris office.

“France [and] its European partners [have] also realized that they don’t have the influence nor the capacity to ‘replace’ U.S. leadership on many … core issues,” she added, noting Macron and others are learning that “geopolitical partners-spoilers like Russia, China or Turkey were actually seeking bilateral confrontation and dialogue with the U.S. — and not with Europe.”

So as Congress returns and judging from the evolution of the Trump-Macron relationship, there might be little lawmakers can do to force any president — but particularly Trump — into playing nicer with allies and being tougher on foes like Putin.