For Trump has also repeatedly diminished not only the reputation of his own office, but that of anyone who would serve him. On his first day in office, he turned Sean Spicer, a veteran, generally well-regarded Republican press spokesman, into a walking punch line because of his insistence that the crowd at Trump’s inaugural was the largest ever. He has reduced Rex Tillerson, once the all-powerful head of one of the world’s largest multinational corporations, to a supplicant secretary of state, whose diplomatic initiatives the president summarily—and publicly—overrules. And he has deployed John Kelly, an admired four-star Marine general, as a partisan political surrogate in a dispute over his handling of the death of a fallen soldier.

Far from draining the swamp of Washington, as he promised, Trump and his administration have persisted in business as usual—or business unusual, in his case, in which he has personally profited from his namesake hotel’s lease on a government building just blocks from the White House, on Pennsylvania Avenue. His commerce secretary has retained a financial interest in a shipping company with business ties to a Russian oligarch and Vladimir Putin’s son-in-law. His treasury secretary sought the use of government aircraft for personal travel. A special counsel is investigating his own son-in-law’s business dealings with Russia.

As he did during his maverick campaign, Trump seems determined, on a near daily basis, to test the truth of his assertion that he could shoot someone on Fifth Avenue and pay no political price. His fellow Republicans—even many of those who once doubted his commitment to party orthodoxy—are sticking by him in the range of 80 percent support. His sharpest congressional critics, like Senators Jeff Flake and Bob Corker have opted to retire, rather than face the wrath of his supporters in re-election battles they might lose. House Speaker Paul Ryan, who waltzed up to the edge of “Never Trump” in the primaries, is now locked arm in arm with the president to pass a tax plan that rewards longtime traditional G.O.P. constituencies.

For better or worse, Trump is also testing the truth of Adlai Stevenson’s rueful assessment that, in America, anyone can grow up to be president, and that’s just one of the risks we take. For Democrats, that’s proved a special challenge. Trump has so thoroughly upended the norms of political discourse and partisan give and take that his would-be adversaries are struggling to find an effective way to counter him. Democrats remain deeply divided, re-litigating last year’s bitter primary battle between Hillary Clinton and Bernie Sanders, and grappling to respond to the concerns of people like the rafts of two-time Barack Obama voters who abandoned the party for Trump. One thing is clear: in the face of Trump’s raw, unfiltered messages, the usual canned, consultant-driven talking points can’t cut it anymore.

Moreover, despite Trump’s worrisome saber-rattling on North Korea—and perhaps the starkest threat of nuclear conflict since the Cuban Missile Crisis—the economy is tootling along at near full employment, the stock market is robust, consumer confidence is up, and inflation remains low. And whatever the public’s view of Trump personally, roughly half of Americans still say they have confidence in his ability to negotiate favorable trade agreements and make good appointments to the federal courts.

The president’s mixed signals on immigration (depending on the day or the hour, either for or against the so-called “Dreamers,” brought here as children) have alternately demoralized his base and confounded would-be Democratic allies in Congress and left his bottom line—in this and so many other matters—ever-shifting and unclear. The laws of conventional political physics would suggest that, absent a major turnaround in his poll standings, Trump should face an uphill battle for re-election, and would be all but certain to draw one or more serious Republican challengers for his party’s renomination. But Trump repeatedly defied such laws all last year, and there is little evidence to suggest that any major figure in his own party will be willing to take him on, much less wrest the G.O.P. leadership away from him.

It is the hoariest cliché of the American presidency that the office makes the man. But within days of taking office, Trump left no doubt that the presidency had not changed him one whit. The weeks and months since then have only confirmed that it is Trump himself who is changing the office. Leave aside his administration’s substantive rollbacks in environmental protection and financial regulation, and its curtailment of administrative support and insurance subsidies for health care—all of which have been real enough, and will have real impact in the months and years to come. The big question now is just how far Trump is willing to go to continue remaking the institution of the presidency in his own mercurial image, and at just what price.