For all the rallies, emailed fund-raising pitches and exhortations on his social media website to support Republican candidates, former President Donald J. Trump was always destined to make the 2022 election about one thing: himself.
And so it was distressing, but unsurprising, to a number of Republicans nationally and in Washington that, on the eve of what many polls are forecasting as a strong night for G.O.P. candidates, Mr. Trump began telling people on Monday that he planned to announce his third presidential campaign that night, at a rally in Dayton, Ohio.
Throughout Monday, Republicans who had pressing election-eve work to do instead spent their time trading text messages and anxious calls about whether Mr. Trump was poised to animate Democratic and Republican voters alike as they prepared to vote on Election Day by putting himself front and center.
A close ally of Mr. Trump’s, Representative Matt Gaetz of Florida, road-tested Mr. Trump’s idea for a Dayton announcement on Twitter on Monday morning, following a predictable pattern in which Mr. Trump spreads word of what he’s thinking in the hopes that it becomes public and generates news coverage.
“To all the press texting & calling me: Trump should announce tonight,” Mr. Gaetz wrote. “His candidates won the primaries,” before adding, “Trump deserves all the credit for this wave election & announcing tonight he will seize it.”
By midafternoon, other Republicans were expressing hope that that plan had fizzled. Advisers to Mr. Trump said privately that they believed he wouldn’t declare his candidacy at the rally, his final event of the midterm cycle and a showpiece for candidates in Ohio, a reliably Republican state.
Among their concerns: The chances that Mr. Trump would be blamed for Republican defeats in some contests would only increase if he were to make himself the center of the national conversation on the eve of the election.
Mr. Trump has been teasing the prospect of another presidential run since the spring of 2021, telling audiences they would be “very happy” or “so happy” with his ultimate decision — seeking to build interest without crossing a legal line and triggering the reporting requirements of a formal candidacy.
More recently, those promotional lines have been ramping up with a marketing expert’s precision, as if the run-up to Tuesday were actually a rollout of a new-and-improved product.
“‘I will probably have to do it again,” he said at a Texas rally two weeks ago. On Thursday in Iowa to support Senator Chuck Grassley’s re-election, he generated more coverage by saying he would “very, very, very probably do it again.” In Pennsylvania on Saturday, he said, “I really want to do it.” And on Sunday in Miami, he told voters to stay tuned one more day, saying, “We have a big, big rally tomorrow night in Ohio.”
In recent weeks, Mr. Trump has discussed with advisers timing an announcement that he is running for president for the week of Nov. 14 — most likely on Nov. 16. He has spoken of doing so at a news conference, but some advisers said that a rally was a more comfortable fit.
One reason for Mr. Trump to go forward with a formal campaign is that doing so could help shield him from the many federal and state investigations he faces, allowing him to attack them as politically motivated.
So far, he has held off after his advisers made the case that the political costs would outweigh the benefits.
Still, there’s little doubt that Mr. Trump wants credit for a strong Republican night. And in a number of cases, he has a right to claim it. J.D. Vance, the Senate nominee in Ohio, was trailing in his Republican primary until Mr. Trump endorsed him, and the former president has helped Mr. Vance win over Trump voters who were slow to embrace him.
Elsewhere, Mr. Trump’s endorsement was a boon in the primary but less evidently helpful in the general election, as it was in the case of Mehmet Oz, the Republican Senate nominee in Pennsylvania, who has prioritized winning over suburban swing voters who take a dimmer view of the former president.
What Mr. Trump plainly dreads is the idea that Gov. Ron DeSantis of Florida, a Republican who is favored to win a second term, could emerge from his re-election campaign with a head of steam — and with the admiration of conservative donors and voters who like his talent for aggressively doing battle with liberals on cultural and social issues, a hallmark of the Trump era, but appreciate that he does so without the dramas that swirled around Mr. Trump, distracting from his political agenda.
And so another rationale for Mr. Trump to declare his own candidacy would be to blunt any momentum that Mr. DeSantis could otherwise gain, from a resounding re-election victory, with the supporters the two men share in common.
Michael C. Bender contributed reporting.