Americans old enough to remember Richard Nixon's sacking of the Watergate special prosecutor, Archibald Cox, can attest that, for many, it was the moment they realised the President really had something to hide.
The same may come to be said about Donald Trump's dismissal of FBI Director James Comey yesterday.
The bureau has been investigating alleged links between Trump's election campaign last year and Russia.
For many readers outside the United States - and indeed for many Americans outside the Washington beltway - this subject has probably seemed somewhat overblown by Democrats looking for excuses for last year's election result.
Certainly it is disturbing if Russian agents are using underhand methods to try to influence Western elections but it is hard to believe they could determine the outcome.
Nor was it particularly surprising that an affable, energetic Russian Ambassador to Washington should have spoken to people close to Trump at every opportunity last year.
Trump's first national security adviser, Michael Flynn, did not have to resign for talking to the ambassador but rather, for misleading Vice President Mike Pence about it. However, Flynn has not gone quietly.
Last month he was reported to be ready to testify to congressional intelligence committees investigating the Trump campaign's possible Russian connections in return for immunity from prosecution.
This week Comey testified to Congress about the FBI's investigation into the alleged connections, and about its investigation last year of Hillary Clinton's emails.
Comey misstated several details on the Clinton case and it is on that pretext that Trump has fired him. It is a pretext that might not stand scrutiny.
Comey's handling of the Clinton investigation managed to infuriate both campaigns last year.
The Republicans were furious in July when Comey announced Clinton would not be prosecuted despite the FBI finding fault with her use of a private email account when she was Secretary of State.
The Democrats were devastated when Comey announced, just a week out from the election, that he was re-opening the investigation to check a former aid's email that had just come to light.
Clinton has recently given interviews castigating Comey for his part in her loss and Trump has been equally insistent that Comey helped her, not just last July but since the election, with what he calls, "the phony Trump-Russia story - an excuse used by the Democrats for losing the election".
Comey has said no more on that subject than that the FBI is looking into it. His dismissal suggests the President is at least trying to silence the FBI or worse, stop its investigation.
If a normal President had taken this step it would be a clear admission of something to hide, but it is possible this President has acted simply because the investigation detracts from his election victory.
Nothing appears to be more important to him than the scale of his achievement as he perceives it.
But by firing the FBI director he has fuelled suspicion of untoward Russian dealings. The questions will not go away.