It was an alternate version of reality, one in which Donald Trump was not losing but the victim of a wide-ranging conspiracy stretching across the country in multiple cities, counties and states, involving untold numbers of people all somehow collaborating to steal the election in ways he could not actually explain.

Never mind that Mr. Trump presented not a shred of evidence during his first public appearance since late on election night or that few senior Republican officeholders endorsed his false claims of far-reaching fraud. A presidency born in a lie about Barack Obama’s birthplace appeared on the edge of ending in a lie about his own faltering bid for re-election.

“If you count the legal votes, I easily win,” Mr. Trump said Thursday night in an unusually subdued, 17-minute televised statement from the lectern in the White House briefing room, complaining that Democrats, the news media, pollsters, big technology companies and nonpartisan election workers had all corruptly sought to deny him a second term.

“This is a case where they’re trying to steal an election,” he said. “They’re trying to rig an election, and we can’t let that happen.”

He convinced few people who were not already in his corner. Most of the television networks cut away from the statement on the grounds that what Mr. Trump was saying was not true.

On CNN, former Senator Rick Santorum of Pennsylvania, a Republican often put in the position of defending Mr. Trump over the years, appeared exasperated as he denounced the president’s loose talk of election thievery as “dangerous” and “shocking” and declared that “counting absentee ballots and counting mail-in ballots is not fraud.”

The New York Post, which published salacious articles on Hunter Biden planted by Mr. Trump’s associates before the election, headlined an article: “Downcast Trump Makes Baseless Election Fraud Claims in White House Address.”

Even Fox News noted it had seen no “hard evidence” of widespread wrongdoing, although it later reversed its position and instructed to not refer to Mr. Biden as “President Elect” and its hosts, including Sean Hannity, went on a tyrant, accusing the nation of “stealing” the election from his friend, Donald.

“There is no defense for the President’s comments tonight undermining our Democratic process,” Gov. Larry Hogan, Republican of Maryland and a critic of the president, wrote on Twitter. “America is counting the votes, and we must respect the results as we always have before. No election or person is more important than our Democracy.”

Former Gov. Chris Christie, Republican of New Jersey and a longtime ally of Mr. Trump’s, likewise disputed the president. “I talk tonight now not as a former governor but as a former U.S. attorney — there’s just no basis to make that argument tonight,” he said on ABC News. “There just isn’t.”

With his presidency on the line, Mr. Trump’s lonely appearance in the briefing room with no allies joining him and only staff members and reporters in attendance underscored how isolated he has become just two days after Election Day. With vote counts in key states turning grimmer even as he spoke, Mr. Trump was poised to end this term in office the way he began his presidential campaign in 2015 — defended most vocally by family members and a few loyalists while Republican leaders held him at arm’s length rather than embrace outlandish claims.

However, Trump has picked up some support from fellow Republicans. After Donald Trump Jr. went after Senator Lindsey Graham, Republican of South Carolina, for not speaking up, the senator went on Sean Hannity’s show on Fox on Thursday night and came to the president’s defense. The Senate Judiciary Chairman told Hannity Thursday he will donate $500,000 to the Trump campaign’s legal efforts to challenge election procedures in multiple states, including Pennsylvania, Michigan and Nevada.

Discussing the ongoing ballot counting in Philadelphia that has shrunk the president’s lead over Democrat Joe Biden, Graham described elections in the City of Brotherly Love as being “crooked as a snake.”

Members of Mr. Trump’s inner circle sounded almost desperate as they sought to threaten other Republicans into backing Mr. Trump. Both Donald Trump Jr. and Eric Trump posted messages on Twitter complaining that Republicans were not standing with their father, especially those who may want his support if they run for president in four years.

“The total lack of action from virtually all of the ‘2024 GOP hopefuls’ is pretty amazing,” Donald Trump Jr. wrote. “They have a perfect platform to show that they’re willing & able to fight but they will cower to the media mob instead.”

“Where are Republicans!” Eric Trump added about an hour and a half later. “Have some backbone. Fight against this fraud. Our voters will never forget you if your sheep!”

But they were among the few who spoke up to echo Mr. Trump’s refrain that he was being denied his due in the form of winning the election, a primal scream emanating from the president that was summed up earlier in the day by his own angry, plaintive, all-caps tweet: “STOP THE COUNT!”