During the Watergate scandal, until now the most outrageous political scandal in American history, the crucial question was drawled by Senator Howard Baker of Tennessee: "What did the president know, and when did he know it?"
Today the question is the same.
This is not about Mike Flynn. It is about the President who appointed him, who earlier considered Flynn for vice-president. The latest revelation of frequent contacts between the Trump team and Russian intelligence should be a wake-up call to Republicans as well as Democrats.
When Vice-President Mike Pence was asked by Chris Wallace of Fox News on January 15 if there had been any contacts between the Trump campaign and the Kremlin, he answered: "Of course not. Why would there be any contacts?"
Great question, Mr Vice-President.
Look, there's a great deal we don't know, but Russian interference in the election is potentially a bigger scandal than Watergate ever was.
Watergate didn't change an election's result - president Richard Nixon would have won anyway in 1972 - while the 2016 election was close enough that Russian interference might have tipped the balance.
We don't know whether the Russians had domestic help in their effort to steal the US election, but here are a few dots that are begging to be connected:
First, the American intelligence community agrees that the Kremlin interfered during the campaign in an attempt to help Donald Trump. This isn't a single agency's conclusion but reportedly a "strong consensus" among the CIA, the FBI and the director of national intelligence.
Second, the dossier prepared by a former MI6 Russia expert outlines collusion between the Trump campaign and Russia. CNN reports that American intelligence has communications intercepts corroborating elements of the dossier, and the latest revelation of repeated and constant contacts between the Kremlin and the Trump campaign give additional weight to the dossier's allegations - although it's also important to note that officials told the Times that they had seen no evidence of such co-operation in election manipulation.
Third, President Donald Trump has been mystifyingly friendly toward Russia and President Vladimir Putin. As Jeffrey Smith, a former general counsel to the CIA, puts it: "The bigger issue here is why Trump and people around him take such a radically different view of Russia than has been the case for decades. We don't know the answer to that."
Fourth, Flynn, before taking office, discussed Obama administration sanctions on Russia with the Russian ambassador. Flynn has now resigned, but he was steeped in the principle of a chain of command; I doubt he made these calls completely on his own. Daniel Benjamin, a former counterterrorism co-ordinator at the State Department who has known Flynn for years, says it would have been out of character for Flynn to do so. So who told Flynn to make these calls? Steve Bannon? Trump himself?
We're back to our question: What did the President know, and when did he know it?
The White House hasn't responded to my inquiries, and Trump lashes out wildly at "the fake news media" without answering questions. He reminds me of Nixon, who in 1974 said Watergate "would have been a blip" if it weren't for journalists "who hate my guts". Soon afterwards, Nixon resigned.
Trump supporters say that the real scandal here is leaks that make the administration look bad. A bit hypocritical? It's dizzying to see a President who celebrated the hacking of his rival's campaign emails suddenly evince alarm about leaks.
Sure, leaks are always a concern, but they pale beside the larger issues of the integrity of the US leaders and elections. Published reports have quoted people in the intelligence community as fearing that information given to the White House will end up in Russian hands, even that the "Kremlin has ears" in the White House Situation Room.
I referred to Trump last year as "the Russian poodle", and we've known for years of Trump's financial ties to Russia, with his son Donald jnr saying in 2008, "We see a lot of money pouring in from Russia."
It's all the more important now that Trump release his tax returns so that we can understand any financial leverage Russia has over him. Yet the same Republicans who oversaw eight investigations of Benghazi shrug at far greater concerns involving Trump and Russia.
"I'm just appalled at how little people seem to care about the fact that Russians interfered in our presidential election, clearly, unequivocally, on the part of one candidate," Michael McFaul, a former ambassador to Russia, told me. "What's more important than that?"
To which I add: Only one thing could be more important - if the Russians had help from within the US.
As I said, there's a great deal we don't know. But we urgently need a bipartisan investigation, ideally an independent panel modelled on the 9/11 Commission. It must address what is now the central question: "What did the President know, and when did he know it?"
The New York Times