It will be a reckoning for President Trump, to be sure, but also for Robert S. Mueller III, the special counsel, for Congress, for Democrats, for Republicans, for the news media and, yes, for the system as a whole. The delivery of Mr. Mueller’s report to the Justice Department on Friday marked a turning point that will shape the remainder of Mr. Trump’s presidency and test the viability of American governance.

Washington has been waiting for Mr. Mueller’s findings for so long and invested in them so much that it may be hard for what he has delivered to live up to the breathless anticipation. But once released, the Mueller report will transform the political landscape, fueling calls for the president’s impeachment or providing him fodder to claim vindication — or possibly, in this live-in-your-own-reality moment, both at the same time.

Democrats on Friday played down the notion that the report would be the final word, fearing that anything less than a bombshell would undercut their own drive to investigate Mr. Trump not only on Russia’s election interference but on the myriad other subjects that have drawn their attention. Mr. Trump, for his part, had engaged in a particularly manic Twitter spree lately, assailing the “witch hunt” and the “hoax” and everyone he blames for them, like his fellow Republicans John McCain and Jeff Sessions, in what some had interpreted as a sign of his own anxiety before the special counsel’s verdict. But he was reported to appear relieved with early reports on Friday.