Donald Trump's decision to fire FBI Director James Comey is simply extraordinary.
It comes as Comey is leading an investigation into whether members of President Trump's campaign colluded with Russia to influence the 2016 election.
In so doing Comey brought a criminal investigation to the doorstep of the White House, and vowed to pursue it "no matter how long that takes".
Parallels are already being drawn to the "Saturday Night Massacre" of 1973, where, in the midst of the Watergate scandal, then President Richard Nixon, dismissed Archibald Cox, the independent special prosecutor.
And he accepted the resignations of Elliot L. Richardson, the Attorney-General, and William Ruckelshaus, the Deputy Attorney-General, after both men refused to accept a deal, related to Watergate, that Nixon was seeking to strike.