He overstated his influence on the special Senate election in Alabama.

Mr. Trump claimed that he brought Luther Strange, the Republican appointed to fill the Senate seat vacated by Jeff Sessions, now the attorney general, “up by 20 points” during the Republican primary race for the special Senate election in Alabama. But that assertion is not supported by the data.

Before Mr. Trump endorsed Mr. Strange for the August vote, Mr. Strange placed second behind Roy S. Moore by two and eight points in two polls, and led the field by two points in another. He was not in “fifth” among the candidates in the Republican primary race, as Mr. Trump said. During the subsequent runoff election in September, Mr. Strange trailed Mr. Moore by an average of 11 points in polls and eventually lost by 9.2 percentage points.

“We can concretely say that Donald Trump’s endorsement, and active campaigning for Sen. Strange, had absolutely no impact on the ballot,” Firehouse Strategies, a Republican polling firm, wrote after the runoff.

He gave a premature estimate of the cost of the wars in the Middle East.

The $7 trillion cost, “as of about a month ago,” that Mr. Trump cited appears to refer to an assessment from Brown University that tallies war appropriations, increases in the Pentagon’s war budget, veterans’ care, increases in spending at the Department of Homeland Security and interest payments. Researchers at Brown estimated in September 2016 that war spending had reached $4.8 trillion and could total $7.9 trillion by 2053.

He falsely claimed to have “essentially gutted and ended Obamacare.”

As part of the tax law, Republicans repealed the Affordable Care Act’s so-called individual mandate that required that most people have health insurance, but that does not amount to a full repeal of the current health care law.

The mandate is, indeed, a core component of the Affordable Care Act. But other vital parts of the current law — the expansion of Medicaid eligibility, rules stipulating insurance policies cover essential health benefits and new taxes to pay for the cost of subsidized coverage — remain intact.

With no evidence, he accused other countries of sending their “worst people” through the diversity visa lottery.

Mr. Trump correctly noted that the man accused of killing eight people in a terrorist attack in October in New York entered the United States from Uzbekistan through the diversity immigration visa program. But he was wrong to draw the sweeping conclusion that other countries use the program to expel the “bad, worse” members of their societies.