Representative Jeb Hensarling of Texas needed a favor: Before retiring, he wanted to anoint a local activist as his successor. Mr. Hensarling, a veteran conservative, reached out to President Trump for help, but the White House hesitated to intervene, according to a person familiar with the overture.
Instead, Mr. Hensarling found a willing ally at Mr. Trump’s right hand: Vice President Mike Pence. Mr. Pence backed the congressman’s favorite, Bunni Pounds, last month in a tweet that blindsided key White House aides.
The eager assistance Mr. Pence provided a senior lawmaker reflected the outsize political portfolio that the vice president and his aides have seized for themselves as the 2018 elections approach. While Mr. Trump remains an overpowering personality in Republican politics, he is mostly uninterested in the mechanics of managing a political party. His team of advisers is riven with personal divisions, and the White House has not yet crafted a strategy for the midterms. So Mr. Trump’s supremely disciplined running mate has stepped into the void.
Republican officials now see Mr. Pence as seeking to exercise expansive control over a political party ostensibly helmed by Mr. Trump, tending to his own allies and interests even when the president’s instincts lean in another direction. Even as he laces his public remarks with praise for the president, Mr. Pence and his influential chief of staff, Nick Ayers, are unsettling a group of Mr. Trump’s fierce loyalists who fear they are forging a separate power base.
In addition to addressing dozens of party events in recent months, Mr. Pence has effectively made himself the frontman for America First Policies, an outside group set up to back Mr. Trump’s agenda. He has keynoted more than a dozen of its events this year, traveling under its banner to states including Iowa and New Hampshire. And Mr. Pence has worked insistently to shape Mr. Trump’s endorsements, prodding him in the contests for governor of Florida and speaker of the House, among others.
Word of the internal tensions is getting out beyond the walls of the White House: one prominent lawmaker said the complaints of high-ranking Trump officials were starting to circulate on Capitol Hill.
“They’re looking for people to stay on the team, not break away from the team,” Senator Lindsey Graham, Republican of South Carolina, said of the Trump side of the West Wing.
Mr. Trump and Mr. Pence remain on good terms personally, and the president has largely welcomed the vice president’s political guidance, according to people close to both men. And Mr. Pence has been intimately involved in planning for the 2020 campaign: He joined Mr. Trump for the meeting where the president told Brad Parscale, a digital strategist in the 2016 election, that he would manage the 2020 race. Mr. Pence stood behind Mr. Parscale, rubbing his shoulders, as Mr. Trump spoke.
Yet in at least two instances, the vice president, Mr. Ayers and other aides have badly overstepped. Mr. Pence recently abandoned an attempt to hire Jon Lerner, a Republican pollster close to Mr. Ayers, as a national security aide, after Mr. Trump discovered Mr. Lerner had helped lead attacks on him in the 2016 election.
The quick dismissal of Mr. Lerner was widely seen as a brushback against Mr. Pence and Mr. Ayers, a way for Mr. Trump’s advisers to signal that they were closely watching the vice president’s office. Two senior White House officials said the Lerner episode made Mr. Trump more acutely aware of what these aides described as Mr. Pence’s empire-building.
Tensions also flared last year, after Mr. Ayers and another Pence aide were reported to have made suggestive comments to Republican donors about planning for an unpredictable 2020 election. Most brazenly, Marty Obst, a senior Pence adviser, told a Republican donor that Mr. Pence wanted to be prepared for the next presidential race in case there was an opening.
For now, Mr. Pence and his aides have found a yawning opening within the West Wing, as Mr. Trump’s principal political aides spend much of their time managing his impulses and vying with each other, instead of overseeing the party and this year’s campaign. While past vice presidents, like Joseph R. Biden Jr. and Dick Cheney, have played important roles maintaining the political coalitions of their ticket-mates, neither man wielded Mr. Pence’s independent influence over an administration’s political network and agenda.
Steering Mr. Pence’s strategy is Mr. Ayers, a 35-year-old operative who is the subject of the most pointed criticism from Trump stalwarts. Mr. Ayers regularly joins Mr. Pence in meetings with the president and has told associates that if aides in the West Wing cannot stay on top of things, his office will step up, White House officials said.
Mr. Ayers again unsettled skeptics in the West Wing this month by poaching a politically savvy aide to Mr. Trump, William Kirkland, to join the Pence team. Mr. Kirkland ran Senator David Perdue’s 2014 campaign in Georgia, and Trump officials believe he will effectively run a shadow political office for Mr. Pence, a setup unheard-of so soon into a new administration.
Mr. Pence’s team is aware of the unease within the White House, and Mr. Ayers recently told one Republican ally that one reason Mr. Pence is so effusive in his public remarks about Mr. Trump — he has recently hailed Mr. Trump as a “champion” for conservatives and branded the recent tax cuts a “Trump bonus” for America — is to tamp down questions about his loyalty.
Alyssa Farah, a spokeswoman for Mr. Pence, said in an email that the vice president’s activities were planned in “close coordination” with Mr. Trump and congressional leaders. She said they had formulated a 2018 campaign plan at a Camp David retreat in January and followed the blueprint since then.
“The vice president’s political and fund-raising travel advances the president’s agenda by aiding targeted candidates and committees during the midterms, which is what the president asked us to do,” Ms. Farah said. “Our team works hand-in-hand with our colleagues and have tremendous respect for the work they do.”
Ms. Farah denied that Mr. Ayers had made comments about displacing the White House political office. “Nick has never said anything of the sort,” she said. She also said Mr. Ayers had not described Mr. Pence as being publicly ingratiating to prove his loyalty: “This is false.”
Marc Short, the White House director of legislative affairs, said in a statement that Mr. Pence was vital to the administration’s political strategy. “The vice president’s tireless efforts to protect the majority in the House and expand our majority in the Senate are essential to our legislative agenda,” he said.
Mr. Pence and his aides, however, have plainly functioned in many cases as allies of traditional Republican Party leaders, at times checking Mr. Trump’s instincts.
In April, after Paul D. Ryan announced he would step down as speaker of the House, Mr. Pence urged Mr. Trump against endorsing Kevin McCarthy, the California Republican who is the House majority leader, to succeed Mr. Ryan. Mr. Pence counseled the president to let congressional Republicans work things out on their own, according to Republicans close to the White House and congressional leaders.
The same month, Mr. Pence weighed in to deter Mr. Trump from intervening aggressively in the race for governor of Florida. The president had endorsed Representative Ron DeSantis, a vocal defender of Mr. Trump and critic of Robert S. Mueller III on Fox News, in a December tweet, and privately told Mr. DeSantis to expect a joint appearance this spring.
But Mr. DeSantis faces a contested primary against Adam Putnam, Florida’s agriculture commissioner and a former House colleague of Mr. Pence. After allies of Mr. Putnam appealed to the vice president, Mr. Pence — along with cautious White House aides — argued against further meddling in the race, according to people briefed on the White House deliberations. Mr. Trump has yet to appear with Mr. DeSantis.
Advisers to Mr. DeSantis remain optimistic that Mr. Trump will intervene again in the race, despite internal resistance.
Even skeptics of Mr. Pence have done little to block him from building his own political apparatus, and some concede he is performing a role that has been left more or less vacant. Mr. Pence formed a joint fund-raising committee with Mr. McCarthy and also created his own political action committee, taking in millions of dollars to give congressional candidates. On Monday, Pence allies sought to tamp down any suspicions of disunity by circulating word via Fox News that Corey Lewandowski, Mr. Trump’s first campaign manager, was signing on as an adviser to the vice president’s political committee.
Jan Brewer, the former governor of Arizona, who introduced Mr. Pence at a Phoenix event convened by America First in early May, said he could operate more freely than Mr. Trump at this point.
“We really, really appreciate him leading our party in that respect,” Ms. Brewer said, adding: “His mission is maybe a little bit different than the president, and he is not under attack 24/7 like the president is.”
The vice president drew wide criticism, and grumbling from White House aides, for hailing former Maricopa County sheriff Joe Arpaio as a “tireless champion of strong borders and the rule of law.” Mr. Arpaio, who is running in a Senate race Mr. Trump’s advisers tried to keep him out of, was convicted of criminal contempt but pardoned by the president last year.
Attendees at the gathering cheered Mr. Pence but said they were drawn to him chiefly because of his association with Mr. Trump.
“I don’t know if he can get the nomination or not,” said Lyle Campbell, a retiree living in Scottsdale. “I like Pence very much, but I’d rather have a woman run — I’d rather have the ambassador to the U.N.”
That would be Nikki R. Haley, the former South Carolina governor who currently employs Mr. Lerner and intended to retain him as a joint adviser with Mr. Pence.
After opening for Mr. Trump at the National Rifle Association’s convention in Dallas on May 4, Mr. Pence earned appreciative but not overenthusiastic reviews. John Ray, a retired medical-equipment executive from Missouri, called him a useful sidekick.
“He brings to the table staunch support of the president,” Mr. Ray said. “And the president needs that.”
Alexander Burns reported from Dallas; Jonathan Martin from Tempe, Ariz.; and Maggie Haberman from Washington.