European leaders and U.S. experts are confused and concerned about what they see as conflicting messages from the Trump White House about policy toward the European Union. They’re not sure whether the administration will support the union in its current form, or encourage more countries to leave it, potentially leading to its disintegration.

This week’s visit to Europe by Vice President Pence to reassure nervous allies contrasted with a series of other events that are calling into question the decades-long bipartisan U.S. policy of E.U. support. Suddenly, the previously fringe view that the European Union is bad for the United States has been thrust into the mainstream foreign policy debate in Washington, and those for and against that idea are gearing up for a battle that could help determine the future of the union and the transatlantic alliance.

“Too much has happened over the past month in your country and in the E.U. Too many new and sometimes surprising opinions have been voiced over this time about our relations, and our common security, for us to pretend that everything is as it used to be,” European Council President Donald Tusk said Monday as he stood alongside Pence in Brussels.

Brussels is counting on the “United States’ wholehearted and unequivocal” support for a united Europe, and Pence confirmed that the United States still endorses that idea, Tusk said.

In his remarks, Pence declared that President Trump had sent him to Brussels to confirm “the strong commitment of the United States to continued cooperation and partnership with the European Union.” Asked directly whether the Trump administration was opposed to more countries potentially leaving the E.U., such as France, he repeated that line verbatim.

While some European officials who met with Pence on his Europe tour said afterward that they did feel reassured, other reports fueled concerns that Pence’s message is not shared by other senior White House officials, including Trump.

Reuters reported Tuesday that White House chief strategist Stephen K. Bannon met last week with Germany’s ambassador to the United States, Peter Wittig, and expressed skepticism about the union while pledging to focus more on bilateral relations with European states. The White House denied the substance of the call and the German Embassy declined to comment. But Bannon has expressed similar views in the past.

Several European diplomats in Munich also conveyed to me strong reservations about reports that Professor Ted Malloch, a proud E.U. skeptic, might be appointed as the Trump administration’s E.U. ambassador. My Washington Post colleagues reported that Brussels has ordered a review to determine how Malloch might be rejected if he is nominated.

In an email exchange, Malloch told me that the E.U. Ambassador to the United States, David O’Sullivan, had personally démarched the State Department to say the E.U. is opposed to his potential nomination. He also said he had heard that E.U. foreign policy chief Federica Mogherini told the Trump administration Brussels would not accept him as ambassador. In a Feb. 19 article for Breitbart, Malloch claimed there is a concerted European effort to stop his candidacy.

A spokesperson for the E.U. mission in Washington told me, “No démarche and no threats of not granting agrément have been made.” In her news conference in Washington, Mogherini said that she was told no final decision on an E.U. ambassador had been made.

“I made clear that, first of all, our procedures require the active consent of all the 28 member states of the European Union for the accreditation of an ambassador and that has to be taken into consideration,” she said.

The State Department declined to comment. The White House did not respond to requests for comment.

If Malloch were chosen, the E.U. would have good cause to believe that the Trump administration is set upon supporting the disintegration of the union. In a Feb. 14 op-ed entitled “The U.S. view of European integration,” Malloch made the case for breaking up the union.

“The Trump administration is steadily making it clear that the U.S. is no longer interested in the old forms of European integration,” Malloch wrote.

The E.U. is bad for American business, investment and security, Malloch wrote. He argued that the Trump presidency changes the diplomatic game in a way that opens the opportunity for the United States to officially support breaking up the union.

“Of course the Transatlantic Alliance must continue. Good European-American relations are absolutely essential. But European integration is not at all in America’s interest,” he wrote.

For longtime E.U.-watchers in Washington, the rise of voices such as Malloch and Trump’s closeness to other E.U. skeptics, including British right-wing leader Nigel Farage, are a wake-up call. The Washington foreign policy community had naively assumed that the United States would always support the continued existence and development of the union.

“We’ve always taken it for granted that it’s a fundamental pillar of U.S. foreign policy and that’s why nobody talks about it and shame on us,” said Julianne Smith, an Obama administration senior official dealing with Europe, now at the Center for a New American Security.

Despite Pence’s assurances, the message that E.U. leaders in Brussels are getting is that the Trump administration does want to disrupt and undermine the union as an institution, Smith said. That’s most concerning because undermining the community has been a strategic goal of Vladimir Putin’s Russia for a long time.

“That’s a fundamental game-changer,” said Smith. “If you now have a U.S. administration that is going to align with Russia against the E.U., that would be a seismic shift. It could potentially issue a crushing blow to the E.U, and would drastically harm the transatlantic alliance.”

The Russia factor is what concerns lawmakers on both sides of the aisle the most. In remarks at the Munich Security Conference, Sen. Lindsey Graham (R-S.C.) warned that Moscow is working to undermine pro-E.U. governments across Europe through political interference similar to what was seen during the recent U.S. presidential campaign.

“To our German friends, you’re next. To our friends in France, they’re coming after you,” he said.

There is a potential middle ground between a Trump administration that fully supports the European Union and one that actively works to undermine European unity to the benefit of Russian strategic objectives. It’s possible the Trump administration will simply be agnostic about the union and take a hands-off approach, said Theodore Bromund, senior fellow at the Heritage Foundation.

“If I had to characterize the Trump administration’s emerging attitude to the E.U., I would characterize it as ‘don’t much care,’ ” he said. “That’s not the same as out and out hostility but it’s many shades different than general support for the institution that most presidents since Eisenhower have had.”

That view is called into question by Trump’s own statements, such as when he praised Britain’s exit from the union in an interview with a British member of Parliament and called the community “basically a vehicle for Germany.” Washington’s current ambassador to the E.U., Anthony Gardner, also said the Trump team called E.U. leaders to ask “what country is to leave next?”

Henry Kissinger is credited with saying decades ago, “Who do I call if I want to call Europe?” The Trump administration may not only abandon the drive to find that answer but may also work to make sure there’s no single number to dial. If the rest of the Washington foreign policy community wants to head off that policy, a full debate over whether or not the survival of the European Union is really in the United States’ interest must begin now.