YUMA, Ariz. — President Trump, fresh from the racially charged storms of Charlottesville, Va., thrust himself on Tuesday into another high-voltage issue, traveling to a sun-scorched border post in southern Arizona to highlight his determination to crack down on illegal border crossings from Mexico.

Mr. Trump’s visit, long scheduled but newly divisive, was also to feature a campaign-style rally in Phoenix on Tuesday evening that has drawn scores of protesters and fanned fears that it could arouse more of the ugly nativist sentiments that exploded more than a week ago in Charlottesville.

The visit unfolded in the shadow of a rumor — knocked down for now by the White House — that Mr. Trump planned to pardon Joe Arpaio, the hard-line former sheriff of Maricopa County, who became a national symbol of the campaign against undocumented immigrants, and whose round-’em-up raids have landed him in legal trouble.

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“There will be no discussion of that today at any point, and there will be no action will be taken on that front,” the press secretary, Sarah Huckabee Sanders, told reporters, referring to a pardon.

The president’s first stop, in the desert city of Yuma, focused more on enforcement than rhetoric. Venturing into a giant hangar, Mr. Trump met with Border Patrol officials, who showed him a Predator drone, a helicopter and a boat that is used to scour the countryside near the border for illegal immigrants.

The officers also displayed items, including a fire extinguisher with a hollow canister and a Coca-Cola carton with a false bottom, that they said drug traffickers use to smuggle narcotics into the United States.

Administration officials showcased the stretch of border as Exhibit A in the value of a border wall. There are now more than 60 miles of fencing along the border near Yuma — the construction of which preceded the Trump administration — which officials said had helped drive down the number of arrests for illegal crossings by more than 40 percent.

Mr. Trump is using these statistics to make the case to Congress for funding a wall along the entire Mexican border. Some Senate Republicans are balking, and Mr. Trump’s political advisers worry that failing to deliver on this signature campaign promise would hurt him with his political base.

“What he’s done so far has worked,” Thomas Homan, the acting director of Immigration and Customs Enforcement, told reporters. “We need funding to make it permanent. We need to build a wall.”

Mr. Homan said the executive orders on immigration signed by the president had helped further stanch the flow of illegal crossings. But the measures he and other officials cited — such as electronic sensors along the border fences — were put in place well before Mr. Trump took office.

Arizona was the site of one of Mr. Trump’s most raucous rallies during the presidential campaign, and if anything, the atmosphere was even more charged on this visit, his first as president.

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The Democratic mayor of Phoenix, Greg Stanton, pleaded with Mr. Trump to put off his trip, saying it would only aggravate racial tensions, coming so soon after clashes between white supremacists and counterprotesters in Virginia.

The list of people in Arizona on Mr. Trump’s enemies list includes both of the state’s Republican senators: Jeff Flake, a longtime nemesis whom Mr. Trump has described as “toxic” and a “flake”; and John McCain, who cast the decisive Republican vote to dash Mr. Trump’s effort to repeal former President Barack Obama’s Affordable Care Act in the Senate.

For his part, Mr. Trump has toggled unpredictably between appealing for unity in the wake of Charlottesville to reaffirming his inflammatory statements of last Tuesday, when he draw a moral equivalence between the white supremacists and those who tried to resist them.

On Monday night, the president prefaced a speech laying out his Afghanistan policy with a call for conciliation, telling the service members in his audience that they symbolized the ideals of individual rights and respect for minorities that are central to the American experience.

“Loyalty to our nation demands loyalty to one another,” he said in the most eloquent part of his 25-minute address. “Love for America requires love for all of its people. When we open our hearts to patriotism, there is no room for prejudice, no place for bigotry and no tolerance for hate.”

Ms. Sanders said she expected the president to start off in a similarly conciliatory vein, when he takes the stage at the Phoenix Convention Center around 7 p.m. local time.

The lack of a pardon for Mr. Arpaio would deprive the rally of a dramatic moment. But Mr. Trump has said he is seriously considering a pardon for the former sheriff, suggesting it could happen later. Mr. Arpaio was found guilty of criminal contempt of court after he flouted an order to stop detaining people his office suspected of being undocumented immigrants.

Mr. Trump was traveling with Stephen Miller, the senior policy adviser who is a prime advocate for hard-line immigration policy, and John F. Kelly, his new chief of staff, who came over from the Department of Homeland Security.

Mr. Kelly, a retired Marine Corps general who ran the military’s Southern Command, also favors a tough approach on immigration. But he is trying to moderate Mr. Trump’s public statements and to impose discipline on a White House that had come to mirror its capricious boss.

The trip, planned several weeks ago, is viewed by the White House as a chance for the president to recapture momentum, after a week that was lost amid the furor over his reaction to Charlottesville.

Mr. Trump’s political operation put out a radio ad featuring the president’s daughter-in-law Lara Trump urging people to attend the rally. She is expected to be on hand for the gathering.

Mr. Trump said nothing to reporters on his visit to the border center. But he seemed to savor the welcome from military families who stood along a rope line at the Marine Corps Air Station in Yuma.

Though the temperature was 107 degrees, Mr. Trump lingered to take pictures and scrawl his name on caps, while his staff and reporters huddled under a wing of Air Force One to escape the blistering heat.