WASHINGTON — As early voting began Monday in Florida, Senator Bill Nelson and Andrew Gillum, who is running for governor, had former Vice President Joseph R. Biden Jr. come to Jacksonville and Tampa to urge Democrats to go to the polls in what are two of the most hard-fought races in the country.
Early voting also started Monday in Texas, and that’s where President Trump spoke in an 18,000-seat N.B.A. arena. But he was rallying support in a pair of less-competitive races: the re-election campaigns of Senator Ted Cruz and Gov. Greg Abbott.
Conspicuously absent from the raucous festivities at Houston’s Toyota Center, where thousands also congregated outside, was the local Republican congressman who is locked in a difficult campaign: John Culberson, whose well-heeled district is full of moderates who recoil from Mr. Trump.
The split-screen between Florida and Texas — one the most crucial presidential battleground in the country, the other a pillar of conservative strength — neatly illustrated Mr. Trump’s role in the fall campaign. He is often away from the center of action, shunned by many of his party’s most vulnerable House candidates but still commands enthusiastic audiences on a scale rarely seen in a midterm election.
Two weeks before the ballots are all counted, and the first verdict rendered on his presidency, Mr. Trump is both overwhelming the campaign with tactics like attacking the migrant caravan but is also detached from some of the races that may determine who controls the House.
While polls show this president is more of a factor in voters’ calculations — pro and con — than his predecessors, Mr. Trump has avoided large swaths of the country. The entire Pacific Coast, much of the Northeast and large interior cities like Chicago, Minneapolis and Kansas City, where Republican lawmakers do not want to be seen with him, are effectively no-go zones.
He is hardly the first president whose unpopularity has limited his campaign travels — there were plenty of candidates who did not want to appear with the last two occupants of the Oval Office. But rarely has there been such a collision between the vanity of a president and the political reality he’s confronting. Mr. Trump is as much a celebrity as he is a politician, and he wants his rallies, which are only nominally about the officeholder he’s in town for, to match the hype of other global celebrities.
Representative Kevin Cramer of North Dakota, whom Mr. Trump personally wooed into running against Senator Heidi Heitkamp, recounted the many conversations he had with the president about his lightly populated state’s stadium-scale venues and said Mr. Trump had his eye on North Dakota State University’s FargoDome.
“‘Do you know how many arenas I’ve beaten Elton John’s record?’” Mr. Cramer recalled Mr. Trump telling him.
The president’s destinations also reflect the competing impulses of his advisers. The White House political director, Bill Stepien, and his colleagues are eager to claim credit for saving as many House seats as they can, no matter how small a market they must send the president to, according to people familiar with their planning.
But the manager-in-waiting for Mr. Trump’s 2020 campaign, Brad Parscale, and his allies are eager to flex the president’s political strength ahead of his re-election bid, and collect as many cellphone numbers and emails as possible — and thus prefer overflowing big-city venues such as the home of the N.B.A.’s Rockets in Houston.
So after his filled-to-the-rafters rally in the country’s fourth-largest city Monday, Mr. Trump on Saturday, on the second-to-last weekend before the election, will find himself in Murphysboro, Ill., a town of 7,568 where Representative Mike Bost could use a lift in a district that is closer to Memphis than Chicago.
Senator Mitch McConnell, the majority leader, said the president’s itinerary recalled former President George W. Bush’s narrowly confined schedule in 2006, at the nadir of the Iraq War, when he was even more broadly unpopular than Mr. Trump is now.
“We could almost take him nowhere,” Mr. McConnell recalled of Mr. Bush. “He ended up going only to the places where he was still in decent shape.”
The Senate map is friendlier terrain for Mr. Trump. The most competitive races are taking place in states where Mr. Trump remains well-liked, or at least is not as toxic as he is in some up-for-grabs House districts.
Mr. McConnell praised him for being “willing to go where he needs to go,” and the president has been in high demand in campaigns for the Senate, where Republicans have a bare one-seat majority.
“I’ve been counting on one more time,” said Mr. Cramer, who polls show is leading in his bid against Ms. Heitkamp.
He is hardly alone: Other Republicans involved in many of the most competitive Senate races are also clamoring for a final visit from Air Force One before Election Day to motivate pro-Trump voters.
“The president is the Trump card in Montana,” said Senator Steve Daines, a Republican who is hoping to help defeat the state’s other senator, Jon Tester, a Democrat. “Another visit from him right before Election Day will further drive G.O.P. turnout and increase support for Matt Rosendale,” he said, referring to Mr. Tester’s challenger.
Most of the president’s hour-plus performances are one-man shows: Unlike with past presidents, the candidate of the hour is handed the microphone by Mr. Trump only briefly sometime during his monologue. Strategists involved in the campaigns have even started to time how long into his remarks it is before the president mentions the race in question and starts attacking the Democrat on the ballot, which is the 30 seconds of footage they most covet.
And Mr. Trump’s desire to fill arenas often overrides the preference of the candidate he is ostensibly there to help. When he visited Pennsylvania earlier this month to endorse Representative Lou Barletta’s Senate campaign, for example, the president chose to appear in Erie rather than Pittsburgh, even though Mr. Barletta’s campaign indicated their preference was Pittsburgh, according to officials close to the congressman, who stressed they were delighted to have the president at all.
For other Republican lawmakers and operatives, though, the Trump rallies are simply hazards to be avoided. In some House races, the president has been forced to appear in second cities — Topeka instead of Kansas City, or Rochester instead of Minneapolis — because the incumbents are attempting to convince their suburban electorate that they are independent of Mr. Trump.
“They’re between a rock and a hard place,” said Thomas M. Davis III, a former Republican congressman from Virginia, of the attempt to balance appeals to upscale anti-Trump voters and the party’s bedrock supporters.
White House aides, who were not authorized to speak publicly about strategy, said that their teams defer to the campaigns in choosing where Mr. Trump can be most useful in their districts or states, and that even the Senate contests he appears in have down-ballot advantages. This week he’s appearing in three districts with open seats, which White House officials believe are at the root of their difficulty this year.
Officials pointed to 17 House districts where Mr. Trump had campaigned by mid-October, and they said that the areas where he appears are spots he can best draw in the nontraditional midterm voters who supported him.
The White House has very much taken notice of who has spurned Mr. Trump — Representative Erik Paulsen of Minnesota and Representative Kevin Yoder of Kansas are mentioned frequently by West Wing officials — and Mr. Stepien even went so far as to write a memo this month warning lawmakers that they would not fare well if they did not “boldly align” themselves with the president.
But that remains an open question in Florida, where Gov. Rick Scott, running for the Senate, has drawn notice in the White House for his willingness to appear with Mr. Trump at official events but refusal to stand with the president at his beloved rallies.
The president is planning a trip to Fort Myers next week, and may return to Florida once more before the election, but it is unclear if Mr. Scott will appear at the rally, which will feature the Republican nominee for governor, Ron DeSantis. Private polling by both parties indicates that the campaigns for governor and senator are, in the typical fashion of Florida, extraordinarily close.
West Wing officials said they are paying attention to what the governor does, and one of Mr. Trump’s most vocal allies in Florida urged Mr. Scott to show up when the president comes to campaign.
“I would definitely urge the governor to join us to rally the troops as early voting gets underway,” said Representative Matt Gaetz.
A spokesman for Mr. Scott did not reply to questions about his plans, but the governor’s advisers have been uneasy with having him on stage because of the president’s penchant for veering well off script and making incendiary comments. And with Mr. Trump ratcheting up his rhetoric against immigrants, and Mr. Nelson linking Mr. Scott to the president in Spanish-language ads, those sensitivities are even more acute.
One senior Republican official with ties to both Mr. Trump and Mr. Scott predicted the governor would likely use his role leading the cleanup after Hurricane Michael as cover to avoid coming to any political events — but this official acknowledged that if it were not for the storm, the governor would likely come up with another excuse to sidestep the risk of standing beside the ever-unpredictable president.