When President Trump fired Acting Attorney General Sally Yates three months ago, the comparisons to President Nixon's Saturday Night Massacre came naturally. In that infamous incident, Nixon retaliated against Archibald Cox, the Watergate special prosecutor who had been demanding access to the president's secret recordings, demanding he be fired. Instead, the president's actions prompted his attorney general, Elliot Richardson, and his top deputy, William Ruckelshaus, to resign in protest and sparked a national furor that ultimately led to his resignation.

For many, the Yates case called back to that crisis point of Watergate. Both moments involved a serious showdown between an embattled president and the top officials at his own Department of Justice, and both culminated with dramatic nighttime dismissals of those same officials.

But as I noted at the time, there was one crucial difference: "Nixon worked to stop an investigation of his administration's own criminal activities, while Trump acted to ensure the enforcement of his executive orders. Given their targets, Nixon's purge represented a clear constitutional crisis in ways that Trump's actions, as of yet, do not." That difference is now gone.

With this afternoon's abrupt firing of FBI Director James Comey, comparisons to the Saturday Night Massacre have been widely renewed and, this time, they are warranted. Just like Nixon, Trump fired the federal official who has been leading an inquiry into his administration's alleged misdeeds. And, just like Nixon, he did so precisely as that inquiry seemed to be closing in on him. The investigated fired the investigator, and all hell is breaking loose.

That's where we stand at the moment, but the comparisons between Trump and Nixon won't end there. We should consider how the presidents acted, but we should also take note of how the nation responded. ...