WASHINGTON ― National Security Adviser Michael Flynn is gone ― that didn’t take long ― but he leaves behind a famous and fateful question: What did the president know and when did he know it?

Donald J. Trump has been president for less than a month, and already the Watergate query is all the capital is talking about, and, as a result, there is a widespread sense of a White House in deep, perhaps cataclysmic, trouble.

The list of failures and missteps of the Trump administration is as well known as it is long: a litany of patently obvious lies to the public and the press; mismanagement and vicious infighting; several malodorous Cabinet choices; mixed messages from on high, many of them coming within minutes of each other; leaks that gush like a fire hydrant; national security lapses that would be comical if they were not so risky; and a job approval rating lower at this point than that of any new president in memory.

But all of that is as nothing compared with the conflagration now.

Flynn resigned after it became clear that federal investigators and the national media were closing in on his close relationship ― bought and paid for, it appears ― with Vladimir Putin and his henchmen in Moscow.

Then-acting Attorney General Sally Yates informed Trump and his circle weeks ago that the FBI had developed information that Flynn had been compromised by his close, and financial, Russian ties.

Kevin Lamarque / Reuters Sally Yates, then acting U.S. attorney general, sounded an alarm weeks ago about Michael Flynn.

But now come some obvious, and, for Trump, perilous, questions.

What did the president know and when did he know it about Flynn’s friendly and potentially compromising calls in December with the Russian ambassador? In those conversations, Flynn allegedly told the Russian to disregard the Obama administration’s imposition of new sanctions, because Trump would lift them once he assumed office.

Is it possible Flynn would have had those conversations with the Russian ambassador and not told Trump about them? Was Trump really flying blind when he praised Putin for not reacting to those sanctions? Who else in the chain of command, as chaotic as it is, knew of Flynn’s conversations and his assurances to Russia?

Now that Flynn is out of the White House, he no longer can claim executive privilege if subpoenaed to testify before Congress. Will he take the Fifth? Possibly. Will he talk? Unlikely.

Yates communicated her concerns to White House Counsel Don McGahn, a longtime Trump adviser whose main qualification was his loyalty to Trump and knowledge of business and campaign finance. He knows little or nothing about national security.

But what chance is there that McGahn would not have told the president about the warning from Yates?

With Flynn gone, who will be national security adviser? Will the role still matter? Will the CIA, which reportedly had considered Flynn a security risk (!) be assuaged?

No one has been prosecuted under the more-than-200-year-old Logan Act, which forbids the private conduct of diplomacy, but if Flynn didn’t tell the truth to the FBI, he could be at risk of prosecution.

Flynn wasn’t the only Russia proponent in the administration. Others include chief strategist Steve Bannon and Secretary of State Rex Tillerson. What did they know and when did they know it? And what have been their dealings with Russia?

Flynn’s departure will also inevitably draw attention back to the role of Russian hacks and leaks in the 2016 presidential campaign ― and to demands, so far turned away by Trump, that he release his tax returns. The president has said that he has no loans from Russia or Russians. Really?

Late Monday, the list of questions continued to grow, and there was a sense in Washington that the real story of the Trump administration was just beginning to be told.