When the history of Donald Trump's presidency is ultimately written, July 16, 2018, will have a special entry.
On a day when the setting called for a show of strength and resolve from an American president, Trump instead offered deference, defensiveness, equivocation and weakness.
If anyone can recall a performance by a US president that rivalled the one seen around the world today, let them come forward.
In the meantime, Trump's extraordinary joint news conference with Russian President Vladimir Putin will stand on its own, for sheer shock value and for the reality of an opportunity lost.
Here was a president turning his back on the collective work of US intelligence agencies, looking the other way at indictments returned last week by Special Counsel Robert Mueller against 12 Russian military intelligence officers who sought to undermine American democracy during the 2016 election, and falling back as he so often has on attacks against Hillary Clinton, criticism of Democrats and boasts about the size of his Electoral College victory.
In reality, he did more than turn his back on the evidence of Russian attacks on the US electoral process. He all but rejected it.
In an attempt to say both sides have their views of what happened during the last presidential election, he proffered that his own view is that he can't bring himself to accept that the Russians did it. "I don't see any reason why [Russia would interfere]," he said.
It is a fiction to which he has reverted from the very beginning of his presidency, in the face of repeated and escalating evidence to the contrary.
In Helsinki, he said that the Russian leader had offered "an extremely strong and powerful denial" of interference and so he would not forcefully offer evidence to the contrary. What he may have said in the private meeting with Putin is lost to history, given the absence of note-takers or advisers present.
One can only imagine Putin's satisfaction at the way things have turned out.
His country's attacks on US democracy have sown internal discord and distrust, setting Americans against Americans. He has watched the US-European alliance come under enormous strain, with the President now branding the European Union a foe.
He watched Trump bow to what the President must assume are the demands of diplomacy - offering public praise and compliments to the Russian, rather than blunt talk when called for - rather than standing up, as Putin did when he was questioned about the interference.
The news conference was the capstone to an international trip in which, at every opportunity, the President undercut US allies in Europe while playing nice with Putin.
He did this through repeated derogatory tweets, backroom hectoring of European leaders (especially German Chancellor Angela Merkel), interviews with the British media (in which he attacked British Prime Minister Theresa May) and the US press and in public settings with other world heads of government.
Together they added up to a moment that will leave a mark on Trump's presidency.
That's not to say it will fundamentally change the course of his presidency, given the fluidity of events, the reality that attention spans are short and the probability of more shocks from various directions that will put the focus elsewhere.
Nothing much changes minds about the President, and this trip and the news conference might not either.
But as a reportable moment, as a measure of character and leadership, what the world witnessed will help to shape ultimate judgments about Trump.
Time and again, in the face of strong and direct questions by two American reporters, Jeff Mason of Reuters and Jonathan Lemire of AP, the President refused to stand up for the country he was elected to represent and protect.
One glaring question that comes out of the moment is whether, in any way, this will affect or alter the posture of Republicans towards the President, especially GOP elected officials beyond the small cast of characters - senators John McCain and Jeff Flake of Arizona, Bob Corker of Tennessee, Ben Sasse of Nebraska among them - who have regularly stood in opposition to many aspects of Trump's policies and comments.
Others have been selective in their critiques, still others largely silent. That's because Trump has so dominated the party that he successfully hijacked in 2016 that Republicans have bent almost completely to his will. That the GOP is a party increasingly in Trump's image is one sign of the strength he has exhibited.
But this is also a Republican Party for whom anti-communism was once an essential ingredient in the glue that bound together an otherwise disparate coalition, and for which scepticism of Russia and particularly of Putin has remained extremely strong. At least until now.
After today's performance by the President, this will become another test of the leaders of a party that once prided itself on being called the party of Ronald Reagan, who was willing to call the Soviet Union the "evil empire" and whose presidency helped bring about the demise of that empire. Will they do any better than the President did in Helsinki? Will they stand up in ways they haven't previously?
Daniel Coats, director of national intelligence, lost little time in responding to the President he serves.
"We have been clear in our assessments of Russian meddling in the 2016 election and their ongoing, pervasive efforts to undermine our democracy, and we will continue to provide unvarnished and objective intelligence in support of our national security," he said.
Others with less direct roles weighed in as well, to reaffirm their belief that Russia in fact was the agent that meddled in the campaign. One was House Speaker Paul Ryan, who said in a statement that "there is no question that Russia interfered" in the election. Yet members of Ryan's conference continue to attack the Justice Department, the FBI and Mueller's team for attempting to carry out a thorough and complete investigation into exactly what happened.
That investigation includes the question of whether there was any collusion with Russians by officials associated with the Trump campaign. The President has said repeatedly, as he did today, that there was no collusion. Perhaps Mueller and his team will reach the same conclusion, if they are allowed to carry on through the end.
But Trump's conflation of the issue of collusion with the question of Russian attacks on the US democratic process continues to undermine the entire investigation, turning what should be a nonpartisan examination of what happened and how the country can be protected from any repeat efforts into a partisan brawl. Today, Trump called the investigation "a disaster" for the United States.
All of which raises the obvious question: If the President's comments in Helsinki reflect his true thinking, if he sees the United States as being as responsible for poor relations with Russia as the Russians are, if he is not willing to stand behind the intelligence agencies sworn to protect this country, what exactly does "America First" really mean?