While President Donald Trump has disrupted assumptions about US foreign policy, members of his Cabinet have been scrambling to reassure allies the United States remains a bedrock of support.

The trouble is, after four weeks of tumult at the White House, the allies are not sure whom to believe.

Trump has questioned the European Union and NATO, spoken admiringly of Russia, and upended Middle East diplomacy. His proxies have maintained that the United States is still a deterrent to Russia and China, a credible arbiter in the Middle East and a faithful ally to Europe.

The skepticism over who is in charge in Washington crystallised Friday at an annual meeting of dignitaries in Munich for a yearly security conference. Germany's defense minister, Ursula von der Leyen, caused ripples when she pointedly expressed appreciation for the US "secretary of defense's strong commitment to NATO."

She was referring to Defense Secretary Jim Mattis, who has spent his week in Europe trying to persuade allies that contrary to what Trump has said in the United States, the country has not soured on the trans-Atlantic alliance.

Several people at the conference instantly took note on Twitter of Von der Leyen's phrasing, including Vali Nasr, dean of the Johns Hopkins School of Advanced International Studies. He wrote, "German Defense Min tells #MSC2017 Europe appreciates Sec Def Mattis strong commitment to #NATO – she didn't say US commitment."

Vice President Mike Pence – who arrived in Munich Friday night – Mattis, homeland security secretary John Kelly and secretary of state Rex Tillerson have all spent much of the week soothing European fears, presenting traditional Republican national security orthodoxy of confronting Russia, supporting NATO and backing democratic institutions.

But every time they seemed to be getting traction in convincing skittish diplomats Trump was not about to abandon decades of US national security policy, their boss did something in Washington that undercut their work.

The result has been confusion among global leaders about whom to believe when it comes to the direction of US national security.

The reassuring message Trump's subordinates have sought to convey has been further undermined by some of his Republican critics.

Republican Senator John McCain, whose disdain for Trump is well known, was quoted as saying at the Munich conference that Michael Flynn's resignation as Trump's national security adviser over his Russia liaisons was "something that shows that in many respects this administration is in disarray and they've got a lot of work to do."

The contradictions have abounded. On Wednesday, Trump seemed to abandon a broad international consensus on how to achieve peace between Israelis and Palestinians, asserting that he was not committed to a two-state solution.

Twenty-four hours later, his UN envoy said, "We absolutely support a two-state solution," adding that the administration simply wanted a "thinking out of the box" approach about resolving one of the world's intractable conflicts.

The same day Trump questioned the two-state approach, Mattis was at NATO headquarters telling allies the commitment of the United States to NATO remained firm. But Mattis also echoed his boss when he warned the United States might "moderate" its support if other member countries did not spend more on the military.

The next day, still at NATO, Mattis was back to saying that the US commitment to NATO was unshakable. He said the Trump administration's "commitment to Article 5 remains solid," referring to NATO's principle that an attack on one is an attack on all.

European diplomats breathed a sigh of relief again, until Trump held a prolonged and chaotic news conference a few hours later in Washington.

"Let's put it this way, the discrepancy between the president's news conference and the way his Cabinet is trying to reassure Europeans couldn't be wider," said Michael Werz, a senior fellow at the Centre for American Progress, who was at the Munich conference.

Volker Perthes, head of SWP, a policy research group based in Germany, said: "Mattis speaks of 'defending the rules-based international order.' I hope he can explain this to his boss."

What appeared to rattle people the most about Trump's news conference Thursday were his attacks on members of the news media assembled before him. Several diplomats said they worried Trump was trying to discredit a tenet of US democracy – a free press – and in so doing, might embolden despots around the world into further challenges to freedom of the press.

Struggling to explain how to assess the seeming chaos coming out of Washington, Michael Fallon, Britain's defense minister, told reporters, "You know, new administrations, you know, can take time to settle down."

In the crowded lounges and refined tearooms of Munich's Hotel Bayerischer Hof, where leaders and top officials were mingling, much of the talk Friday was not about the panels on issues like "the future of the European Union: united or divided," or "the future of the West: downfall or comeback?"

Instead, it was about Trump's Thursday news conference, which appeared to deeply unnerve several officials.

Overheard conversations included one in which one European official said the United States was on the list of "risk factors" for Europe, echoing a concern expressed two weeks earlier by Donald Tusk, head of the European Council. German officials joked that US diplomats and civil service organisations could qualify for German democracy funding – money designated for countries with struggling democratic institutions.

Several people seemed on edge awaiting what Mattis would say when he addressed the conference. When he finally approached the lectern, he sounded exactly like numerous other US chiefs who have preceded him.

"The trans-Atlantic bond remains our strongest bulwark against instability and violence," he said. "I am confident that we will strengthen our partnerships, confronting those who choose to attack innocent people or our democratic processes and freedoms."

Mattis, Nasr said after the speech, "is the one island of stability." But, he added, "the key is that nobody knows the extent of his influence. Right now, we're tight with trans-Atlantic unity, but who knows what to believe?"