SAN LUIS, Ariz. - President Donald Trump toured a border fence along the U.S.-Mexico divide here Tuesday, seeking to tout what he views as a key reelection accomplishment in a critical state as his bid for a second term has been upended by a resurgent pandemic, an economic crisis and racial unrest.

Trump, who has increasingly focused on immigration amid the coronavirus crisis, said he was marking the 200th mile of border wall erected since his election and reviving one of the most contentious issues of a first term now defined by more pressing challenges.

"It's never mentioned anymore - the wall is never mentioned anymore," Trump said during a roundtable in Yuma, Ariz. "The reason it's not mentioned - it's not that we won the battle. It's that it's such a compelling thing to have done. Because you see the number, and where that wall is going, as you're seeing, it's like magic."

While visiting the border, Trump put his signature on a plaque attached to the barrier.

The trip - more than three hours on Air Force One to a state dealing with a record-high spike in coronavirus cases - was itself controversial because Trump and his aides continued to flout public health guidelines at the same time that top administration officials were testifying before Congress about the growing threat of the coronavirus, which causes the disease covid-19.

Neither Trump nor his aides wore masks during the visit to Arizona, which included the border wall tour and a speech to a crowded group of young supporters in Phoenix. Public health officials have argued against unnecessary travel and several testified Tuesday about the need to maintain social distancing and other preventive measures.

Calling the coronavirus pandemic the "greatest public health crisis" that the United States has faced in more than a century, Centers for Disease Control and Prevention Director Robert Redfield urged Americans to continue taking preventive measures to control the spread of the disease.

"Right now, the most powerful weapon against this disease are social distancing, face coverings and hand hygiene," Redfield told lawmakers.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and a member of the White House coronavirus task force, told lawmakers that Arizona was among states seeing a "disturbing surge" in new cases.

Trump did not spend much time speaking about the coronavirus during his trip to Arizona, despite the state's rapidly rising caseload. On Tuesday, Arizona recorded a record 3,593 new known cases of the virus, as well as a rolling average in new infections 77% higher than last Tuesday's. The state is now reporting 2,136 hospitalizations, more than double the number at the beginning of the month. Hospital bed usage and intensive care unit usage are at 83% and 84% capacity, respectively.

The president focused on touting his immigration record and sought to convince voters in Arizona to back his 2020 reelection bid. Political consultants list Arizona as one of the most important states in the November elections, and Democrats are trying to defeat Trump and Republican Sen. Martha McSally. Both have slipped in the polls in recent weeks, and Trump has visited the state twice even as the pandemic sharply restricted his travel schedule.

"We need you in Washington. Will you please win?" Trump said to McSally during the roundtable. "Because we need you. The alternative that's running against you is not the person that we want."

Democrat Mark Kelly, who is challenging McSally, has been leading in recent polling in a state some Republicans consider key to their quest to keep the White House and maintain control of the Senate. His campaign did not respond to a request for comment.

Trump has pushed a hard-line immigration message as he has attempted to revitalize his campaign after a series of setbacks. In the past week, the president has issued a proclamation curbing immigration visas through the end of the year and decried a Supreme Court ruling that blocked his attempt to end a program shielding some undocumented immigrants from deportation.

Trump's visit to the border was the latest in a series of similar trips in which he has inspected the barrier at various stages of its development since 2017.

The Trump administration has completed more than 220 new linear miles of border barriers, according to the latest U.S. Customs and Border Protection figures. CBP officials say they remain on track to deliver on the president's promise to complete 450 miles by the end of the year, but to meet that goal they will need to increase the current pace of construction to roughly 40 new miles per month.

As construction crews race to meet Trump's objectives despite the pandemic and the desert's withering summer heat, the project has essentially split into two. The administration has been laying down new 30-foot-tall steel barriers relatively quickly on federally-controlled land in Western states, including national forests, wildlife preserves and military bases. But progress has been much slower along the lower Rio Grande in South Texas - the areas considered to be the highest priority to the CBP - because the land there is almost entirely in private hands.

The government has been using its eminent-domain authority to gain access to that land, but the slow pace of property seizures has frustrated Jared Kushner, the president's son-in-law and senior adviser, whom he has tasked with overseeing wall construction.

The president continues to view the project as an asset to his reelection bid and tangible proof of his ability to deliver on promises he made during his 2016 campaign that were widely mocked and dismissed as unrealistic.

More than three years later, Trump's border wall has morphed into one of the most expensive federal infrastructure projects in U.S. history. The White House has obtained $15 billion for construction so far, two-thirds of which has been diverted from Defense Department construction funds and counternarcotics programs over the objections of Democrats and some Republicans.

On Tuesday, the president put his signature to a section of the barrier that has recently been coated in black paint. Trump has been pushing for years to have the entire structure painted, telling aides that it will discourage climbers by making the metal too hot to touch. The cost of painting the wall across hundreds of miles of deserts and mountains is projected to add $500 million to the project's price tag while increasing the structure's long-term maintenance requirements.

Presumed Democratic presidential nominee Joe Biden has said he will halt work on the project if elected, potentially stopping the bulldozers and excavators in their tracks with hundreds of miles of planned barriers left incomplete.

Trump singled out Biden for a political attack during the official White House event in Yuma.

"The Biden people - and he's controlled totally by the radical left, as you understand, he's not controlling it, they're controlling him - they want open borders, they want criminal sanctuaries, they want everything that doesn't work," Trump said. "I don't even think it works politically, frankly."

Biden has criticized Trump for "creating a humanitarian crisis" at the border and slammed the latest immigration restrictions as an "attempt to distract" from a failed coronavirus response.

Trump was scheduled to speak later Tuesday in Phoenix at a Students for Trump rally at Dream City Church, which according to local news can hold about 3,000 people. Arizona doctors raised alarms about the planned mass gathering, which occurred as many of the new coronavirus patients filling up local hospitals have been younger.

Phoenix-based members of the Committee to Protect Medicare, a national network of doctors that's lobbied against Trump, joined a chorus of voices urging caution.

"This is a public health issue. It's not about young or old, it's not about being Republican or Democrat," said Jagruti Patel, a critical care pulmonologist at HonorHealth in Phoenix who says her hospital's intensive care units are 90% full. "It's about human safety."

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The Washington Post's Lena H. Sun, Yasmeen Abutaleb and Hannah Knowles contributed to this report.