The most important relationship in the White House should be the one between President Trump and Vice President Pence. By the accounts of those around the two leaders, that bond is extremely strong. Which makes it even more inexplicable that Pence was kept in the dark during what became one of the biggest headaches to hit the new administration.

Pence is in Europe this weekend, representing the administration at the Munich Security Conference and later at several meetings in Brussels with U.S. allies. He offered assurances Saturday, in the name of the president, that the U.S. commitment to NATO is unwavering, while calling on European countries to step up their financial contributions to the alliance.

With questions about Trump and Russia swirling, Pence said the administration would hold Russia accountable for its aggression in Ukraine while noting the president’s desire for a better relationship with Moscow.

[Pence seeks to reassure allies at Munich conference]

Pence’s message was similar to that delivered earlier in the week by Defense Secretary Jim Mattis and no doubt was welcomed by European allies uneasy and unnerved by what Trump has said over many months about NATO, Europe, Russia and Brexit — Britain’s vote to leave the European Union.

Vice President Pence and German Chancellor Angela Merkel stand next to each other at the 2017 Munich Security Conference on Feb. 18. (Johannes Simon/Getty Images)

Those allies also are wondering whether anyone truly speaks for Trump. On that question, Pence arrived in Europe shadowed, at least to some extent, by what had just happened back home with regard to former national security adviser Michael Flynn.

Basic facts are well known. In January, Flynn personally assured Pence that he had not talked about U.S. sanctions during a December phone call with Russian Ambassador to the United States Sergey Kislyak. Pence repeated that version on national television. Trump and senior White House officials were later told by the Justice Department that Flynn had in fact discussed sanctions and therefore had lied to the vice president.

Nobody in the White House bothered to tell Pence that, if only to prevent him from repeating what he had said earlier. Instead, Pence learned that Flynn had misled him two weeks later, after The Washington Post published a report revealing that sanctions were discussed and in which Flynn backed off his previous denials.

But if basic facts are known, they are not fully known. If there is a simple explanation for what happened to Pence, White House officials have not been willing to share it. Some of those contacted about the matter did not respond. Others said they could not say exactly who made the decision not to share with Pence that he had been misled. No one was willing to speak for the record about sensitive internal deliberations.

That leaves questions: Was it a deliberate decision to keep the vice president out of the meeting where the information was first shared? Why didn’t the president ever mention this to his vice president? Was it poor judgment on the part of some senior official not to tell Pence what had been learned? Was it the result of a sloppy White House operation? Finally, what role did Pence play in triggering Flynn’s forced resignation?

One person who knows Pence described the vice president as seeming to be as aggravated over the Flynn episode as someone with Pence’s calm and moderate Midwestern temperament ever gets. Others closer to the vice president say that’s an exaggeration of the outward emotions the vice president has displayed over the past week or so, as events finally forced the president to dismiss Flynn.

One account has Pence weighing in forcefully last Monday, once the president was back from a weekend in Florida, to register his displeasure at being misled and that his displeasure hastened Flynn’s downfall. Another account suggests there was no notable difference in Pence’s demeanor between Friday morning, when he confronted Flynn about being misled, and Monday, when the discussions hardened into the decision to cut Flynn loose.

President Trump, Treasury Secretary Steve Mnuchin, his fiancee Louise Linton, and Vice President Pence participate in a ceremonial swearing in at the White House on Feb. 13. (Jabin Botsford/The Washington Post)

What recommendation Pence gave to the president is also not known. Aides say the two men talked repeatedly about the matter over a period of days, once it was public knowledge that Flynn had talked to Kislyak about sanctions. The president asked Pence what he should do, according to one Pence adviser, but the vice president, through that adviser, declined to share any of his private conversations with the president.

The president has contributed to some of the confusion about the decision to let Flynn go. The day after the resignation, White House press secretary Sean Spicer said Flynn was forced to resign because there had been a lack of trust that had built up between the national security adviser and the president.

On Wednesday, at a joint news conference with Israeli Prime Minister Benjamin Netanyahu, Trump praised Flynn and said the media had treated him unfairly. Trump’s praise may have been an effort to mollify Flynn, who was reportedly incensed over Spicer’s version of events at Tuesday’s briefing.

By Thursday, at his lengthy news conference, the president was back to the Spicer explanation, that he had lost trust in Flynn in large part because of what Flynn had done to Pence. Still, no one has said why Pence had to learn about Flynn’s lie to him through the media.

[Pence is above the fray but is he outside the inner circle?]

What happened to Pence raised questions in the minds of people who know and care about the role of the modern vice president, a model that has existed since Walter F. Mondale served as vice president to then-President Jimmy Carter.

Joel Goldstein, a professor at Saint Louis University School of Law and author of “The White House Vice Presidency,” said that, at a minimum, Pence should have been in the room when White House counsel Don McGahn briefed Trump and other senior officials about what the Justice Department had told him about Flynn.

“The vice president’s usefulness to other people depends in part on his standing with the president,” Goldstein said. Looking to Pence’s trip this weekend, he added, “Some of those people [in Europe] must be wondering what does it mean that the president didn’t even give him a heads up.”

Pence’s aides said the vice president enjoys the same relationship and understandings with Trump that vice presidents since Mondale have enjoyed with their presidents. He has a standing weekly lunch or private meeting with the president. His chief of staff attends daily White House senior staff meetings. When Pence is not able to attend a national security meeting, his national security adviser attends.

Whether Pence has unimpeded access to all information available to the president — as Richard Moe, who was Mondale’s vice presidential chief of staff, said all past vice presidents have had — is called into question by the failure to alert him to what the Justice Department had conveyed to the White House.

Aides said Pence goes in and out of the Oval Office regularly when he and Trump are in the White House. Beyond that, one senior adviser said, the president and vice president have become good friends, despite having started out their journey barely knowing each other. They say they have not pushed back against the idea that Pence is somehow out of the loop, because it’s something they have no worries about.

“It is purposely set up that both the president’s operation and the vice president’s operation work together,” one Pence adviser said. “I would say this was an honest miscommunication early in an administration.”

On Friday, Senate Majority Leader Mitch McConnell (R-Ky.) was asked whether he thought Pence had been treated badly in the Flynn episode. “Mike Pence had been the indispensable player,” he said. “Yeah, he’s a huge value added for us. We all know him. He has, I think we’ll all stipulate, a very different kind of personality from the president and he’s in the middle of everything and it’s been great. I mean, I think he’s been terrific.”

That’s a view widely shared among congressional and other Republicans and is vital to their ability to retain confidence in the Trump administration. Perhaps this episode was, as Pence’s team says, “an anomaly” in a White House whose growing pains have been on clear display. Pence is unquestionably loyal to the president. But for Pence to be indispensable in his role, he needs a reliable partner in the president, someone who is consistent in his views and doesn’t undercut those around him. Whether Pence can count on that is an open question.