President Trump and German Chancellor Angela Merkel participate in a joint news conference in the East Room of the White House on March. 17. (Jabin Botsford/The Washington Post)

During his presidential campaign, Donald Trump summed up his approach to foreign policy this way: “We must as a nation be more unpredictable.”

But now that he is commander in chief, anxious allies say that unpredictability might be better described as incoherence — a dangerous tendency at a moment of high tension with Russia and Syria, and with U.S. warships heading toward the Korean Peninsula.

In recent weeks, the president has held meetings with his counterparts from other countries. But in some cases, those sessions have only heightened doubts that Trump has a clear sense of what direction he intends to take U.S. foreign policy.

Few if any world leaders, for example, have had as much experience in dealing with U.S. presidents as German Chancellor Angela Merkel, who is on her third.

During their White House meeting last month, Merkel tried to pin down Trump on one of the top concerns of U.S. trading partners: a proposed “border adjustment tax” to be imposed on imported goods. Publicly, Trump has signaled an openness to the idea, but he also said it has drawbacks.

President Trump and Chinese President Xi Jinping walk at the Mar-a-Lago estate in West Palm Beach, Fla., on April 7. (Jim Watson/AFP/Getty Images)

“Don’t worry,” Trump told Merkel, holding his thumb and forefinger close together. “It will only be a little bit.”

Trump’s breezy answer — and Merkel’s exasperation — has been the talk of diplomatic circles in Washington and Europe.

“So all the chancellor of Germany knows is that, ‘It will only be a little bit,’ ” said a senior European diplomat in Washington, holding up his fingers as Trump did, and repeating an account confirmed by others in anxious embassies in Washington. “It’s very puzzling.”

The White House did not reply to a request for information about the exchange between Trump and Merkel.

Ambiguity has always had a place in diplomacy, of course. But Trump adds to that a freestyle approach to international relations. He has a disregard for norms and protocol, an impulsive nature and a tendency toward making contradictory statements.

Compounding the chaos is the fact that those who claim to speak for Trump — Cabinet officials and top White House advisers — also have offered conflicting pronouncements on basic questions about the direction of U.S. policy.

[With both the U.S. and North Korea saber rattling, is conflict imminent?]

President Trump and Jordan’s King Abdullah II hold a news conference in the Rose Garden of the White House on April 5. (Jabin Botsford/The Washington Post)

Trump aides boasted, for instance, of a “positive” chemistry between Trump and Chinese President Xi Jinping during their two-day session at Trump’s Florida resort over the weekend.

But there was no apparent progress on U.S. efforts to have China put pressure on North Korea. And by Tuesday, Trump was engaging in diplomacy via Twitter.

“I explained to the President of China that a trade deal with the U.S. will be far better for them if they solve the North Korean problem!” he tweeted, suggesting that national security concerns might override his long-standing promise to crack down on Chinese trade practices.

Four minutes later, Trump followed with another tweet suggesting he might be leaning toward unilateral action: “North Korea is looking for trouble. If China decides to help, that would be great. If not, we will solve the problem without them! U.S.A.”

In interviews over the past few weeks with a half-dozen foreign ambassadors based in Washington, most complained — diplomatically, of course — that thin lines of communication have made it difficult for them to explain U.S. intentions to officials in their home capitals. That is creating strain on traditionally solid alliances, they said.

“Nobody can tell us on Russia what the American policy is, on Syria what the American policy is, on China what the American policy is,” one ambassador said. “I’m not sure there is a policy. They will listen to me and tell me, ‘We will get back to you when there is a policy.’ ”

The ambassadors spoke on the condition of anonymity to avoid straining relations with the new administration. Or as one put it: “We don’t want to be too hard on them at the very beginning.”

The diplomats said the problem was partly caused by a new administration still in transition and focused on health care, tax reform and other domestic issues. But as the weeks have passed, allies are growing more concerned that limited communication could lead to misunderstandings if a diplomatic or security crisis erupted somewhere in the world.

“I don’t know what will happen,” one said. “You had a president who took three months to take a decision, and now you have one who takes three seconds. It’s very worrying.”

[Trump confronts the contradictions of his foreign policy rhetoric]

Several diplomats said that early Trump meetings with Merkel, Japanese Prime Minister Shinzo Abe and British Prime Minister Theresa May also raised concerns over Trump’s unorthodox style of working largely without detailed notes and speaking off the cuff.

“He doesn’t have a paper in front of him. . . . It’s up to the visitor to declare the agenda,” one said. “He just sits there. It’s like you are in a bar, and you just start talking to him.”

White House officials insist that the president has been fully briefed before his meetings with foreign leaders, and that adequate advance work has been done in bilateral sessions that precede them.

But they also note that the specifics of Trump administration policy are still a work in progress.

“It’s the early days. A lot of this stuff hasn’t been worked through,” said Michael Anton, who runs communications for the National Security Council.

Trump’s priority in these early meetings with foreign leaders, Anton added, is “relationship-building, airing the issues.”

While some diplomats and leaders puzzle over how to decode an opaque and often contradictory presidency, they have figured out one language to which Trump responds: flattery.

In his joint appearance with Trump, Jordan’s King Abdullah II lathered the president with praise for a “holistic approach” to the Middle East, which he said is “a move in the right direction.”

It was their second meeting since Trump’s election, and Trump returned the compliments, calling Abdullah a “warrior.” Their joint news conference was the first of Trump’s presidency to be held in the Rose Garden.

[Secretary of State Rex Tillerson spends his first weeks isolated from an anxious bureaucracy]

Outside of choreographed photo ops, the day-to-day situation is far different.

Several envoys described frustration at the slow pace of appointments to critical jobs, especially in the State Department, which has sometimes left them struggling to get even the most basic information.

“When you reach out to them, it’s like you are reaching out to a body that has a head and legs but no torso. The blood is not flowing from above to below,” one said.

State Department spokesman R.C. Hammond said that a transition is underway that will “continue on for many months.” He added that both Trump and Secretary of State Rex Tillerson are determined to find a new way of conducting international relations because the old one was not working.

“People are starting to learn the new language,” Hammond said of foreign diplomats who deal with the State Department. “They should be encouraged, because there’s great opportunity.”

The ambassadors said communication with the Pentagon and the National Security Council is better, and they uniformly expressed respect for national security adviser H.R. McMaster and Defense Secretary Jim Mattis. But even at those agencies, they said, information on U.S. economic, trade and security policy is often hard to get.

Another channel is Trump’s chief economic adviser, Gary Cohn, to whom diplomats are turning for information on economic policy, including the border adjustment tax.

Cohn has been responsive and seems to have the president’s ear, one diplomat said. “For us, he’s been the guy.”

If a foreign policy crisis were to flare, perhaps over North Korea or Iran, several ambassadors expressed worry that the lack of the usual contacts at many levels of government could keep them from being able to fully explain Trump’s actions to their leaders back home.

[Trump talked tough about China but is now struggling to deliver on his trade promises]

One ambassador said that when he approached the State Department and the White House recently, he was told to come back if he has an emergency to discuss.

Several added that they have tried to be creative in their approaches to the Trump administration, increasingly going outside the normal channels. Some said they have tried to leverage friendships with people in business who have ties to Trump son-in-law Jared Kushner or daughter Ivanka Trump to get access to those key members of Trump’s inner circle.

What entree exists is generally limited to ambassadors talking to top White House officials, without the traditional bureaucrat-to-bureaucrat relations at lower levels where work is usually conducted.

“I have never had trouble getting access,” one ambassador said. “But when we have visitors below the top levels, like members of parliament, we can’t find interlocutors for them.”

The envoys said Trump has made efforts to create ties with the foreign diplomatic corps, including many at the Mar-a-Lago for the Red Cross Ball on Feb. 4.

But they said the transition period had been unlike any they had ever seen.

“The question is: Will the close allies maintain that same natural cooperation that we have had for 70 years?” one ambassador said. “The leaders of those allies want to maintain a relationship of trust with the traditional leader of the Western world. But today we have the impression that the chair of the leader of the Western world is a little bit empty. We are reaching out to test those relationships, but we have no answer.”

Said another: “It’s quite distressing that the Americans are so unpredictable. Unpredictability is the worst.”

Anne Gearan contributed to this report.