Donald Trump has been hacking away at the foundations of international order for months.
Monday may turn out to be the day when he finally succeeded in cracking it open.
Faced with a direct question as to who he believes — the U.S. intelligence agencies he oversees or the autocratic leader of a powerful rival state — Trump ducked and dodged and then finally gave the benefit of the doubt to the longstanding foe of his own country.
This would be extraordinary enough if it was a one-off event. But of course it isn't.
Trump has been on a campaign to destabilize and eventually destroy the United States' traditional alliances and the international institutions it has built over the past six decades.
Faced with a persistent trade deficit with China, he launched a self-destructive trade war against the United States' closest economic partners — Canada, Mexico and the European Union.
He went to the G7 summit in Quebec and thumbed his nose at Washington's major allies, personally insulting Prime Minister Justin Trudeau in the bargain.
He wrote off the NATO alliance as "obsolete" and said he'd be just fine if it broke up. And last week alone, he publicly dissed the leaders of two more major U.S. allies, Germany and Britain.
If Trump had deliberately set out to shred any trust that Washington's allies may still have in American leadership, he couldn't have done a better job.
Yet on Monday he outdid himself after his two-hour meeting in Helsinki with Russian President Vladimir Putin.
Trump went into the meeting only three days after the U.S. special counsel investigating Russian meddling in the 2016 presidential election issued indictments of 12 Russian intelligence officers.
The indictment, reported the New York Times, "includes a litany of brazen Russian subterfuge operations meant to foment chaos in the months before Election Day." And further, "it details a vigorous and complex effort by Russia's top military intelligence service to sabotage the campaign of Mr. Trump's Democratic rival, Hillary Clinton."
On the same day, Trump's own top intelligence official, Republican Dan Coats, told a Senate committee that the Russians are still at it. "The warning lights are blinking red again," said Coats. "Today, the digital infrastructure that serves this country is literally under attack."
Faced with all that, and asked pointedly whether he believed Putin's denials of meddling or the evidence of his own intelligence agencies, Trump meandered on about Hillary Clinton's lost emails and then effectively came down on the side of — Putin.
He said "I don't see any reason why it would be" Russia that was responsible for campaign interference. He stressed that Putin was "extremely strong and powerful" in denying any involvement. At no point did he tell the Russian president to his face to cease and desist from interfering in American elections.
The contrast between Trump's kid-glove treatment of the Russian autocrat and his back-of-the-hand contempt for the leaders of Washington's democratic allies could hardly be more stark.
It's clear now that Trump is most comfortable with tyrants and dictators, men he obviously admires and believes share his values. He has no use for mere democratic leaders, hobbled as they are by parliaments, courts and opposition groups. There's no reason to think this will change.
The question now is whether the president has crossed a line for honorable Americans who have generally supported him so far. A few Republican politicians denounced his siding with Russia over U.S. intelligence agencies as "shameful" and "disgraceful," but they have criticized him often before without actually doing anything to rein him in.
If that pattern continues, Trump will wreak untold havoc on America's standing in the world, not to mention make it that much more difficult to protect U.S. elections from Russian manipulation.
Some are calling that treasonous. If it isn't quite that, it's the closest thing to