On May 9, President Donald Trump fired FBI Director James Comey, the official who was leading a federal investigation into questionable, and possibly illegal, connections between Mr. Trump and the Russian government. The firing is eerily reminiscent of the “Saturday Night Massacre,” the evening in October 1973 when President Nixon ordered the firing of Watergate special prosecutor Archibald Cox.

Mr. Trump’s decision to fire Comey is only the latest in a long line of decisions, statements and never-ending stream of tweets that have raised the most serious questions about Mr. Trump’s fitness to serve as president of the United States, the most powerful office in the world. Only a day before Mr. Trump fired Comey, we learned that both President Obama and former acting Attorney General Sally Yates had personally warned Mr. Trump and his White House counsel of very serious concerns they had about Michael Flynn becoming national security adviser. Obama and Yates had sound reason to believe that Flynn was dangerously compromised, and possibly subject to blackmail, by the Russian government. Yet Mr. Trump hired Flynn anyway—only to fire him 18 days later.