President Trump attends a meeting with law enforcement officials about the MS-13 street gang and border security, at the White House on Feb. 6. (Jabin Botsford/The Washington Post)

Donald Trump has taken the presidency to yet another new low.

In a remarkable set of tweets over the weekend, the commander in chief sounded off on new revelations about the extent of Russia’s campaign to undermine our electoral system. His response: to lash out at his political adversaries and the institutions that are charged with keeping the country safe.

What was missing — tellingly so — was any indication that he plans to do anything against the perpetrators themselves.

Imagine how history would have judged Franklin D. Roosevelt in the aftermath of Pearl Harbor, if he had taken to the radio airwaves to declare that Tokyo was “laughing their asses off.” Or if George W. Bush had stood in the rubble of the World Trade Center with a bullhorn and launched a name-calling tirade against the Democrats.

There was no loss of life or destruction of a city in the Russian actions described in a sweeping indictment secured by special counsel Robert S. Mueller III. But it was an act of war nonetheless, a sneak attack using 21st-century methods.

These are the moments that test a country — and a president. They call for bringing people together in a sense of national purpose against a common adversary.

Once again, Trump has failed that test. He even went so far as to exploit the tragic Parkland, Fla., school shooting, which might have been prevented, had the FBI heeded warnings about the troubled young perpetrator who killed 17 people.

“Very sad that the FBI missed all of the many signals sent out by the Florida school shooter. This is not acceptable,” the president tweeted. “They are spending too much time trying to prove Russian collusion with the Trump campaign – there is no collusion. Get back to the basics and make us all proud!”

His claim was grotesque and baseless, even by Trumpian standards. His self-absorption is such that he cannot see beyond his own fixation, which is that all of this has no meaning beyond the legitimacy of his own election.

Moscow must indeed be laughing.