Acting Homeland Security secretary Chad Wolf signaled that the United States could experience an increase in migration and an “unimaginable public health crisis” at the U.S.-Mexico border if President Trump loses the election and his hard-line immigration policies are overturned.\

Wolf spoke to law enforcement officers Thursday in Arizona, a battleground state in the coming election, as Trump prepared for the final presidential debate against Joe Biden in Nashville.

A former lobbyist still awaiting Senate confirmation, Wolf said Trump has tamped down attempted border crossings, curbed asylum fraud, and worked with a “singular focus” to protect American jobs. He said Trump has completed 400 miles of border wall and has persuaded Mexico to host more than 65,000 migrants awaiting U.S. asylum hearings, preventing them from absconding inside the United States.

Without mentioning Biden by name, Wolf said a change in leadership could reverse those gains. October could be one of the highest months for illegal crossings “in some time,” he said, without providing more details.

“The only reason today’s crossings have not reached a crisis level is because of the policies and procedures the department has put in place over the past four years,” Wolf said in his speech to the Arizona Sheriff’s Association in Phoenix. “If these critical tools are removed or overturned, then the department — and you, our front-line partners — would be imperiled by another immigration crisis.”

Biden campaign spokesman Michael Gwin criticized Wolf’s speech, saying he was “engaging in partisan politics” amid a pandemic.

He said Biden would enforce the law without the extremes that roiled the Trump administration, which drew condemnation in 2018 for separating migrant parents from their children to discourage mass migration.

“The truth is that Vice President Biden will reform our broken immigration system by taking smart steps to secure our border, while still upholding the basic American values that Trump and Wolf have so callously tossed aside,” Gwin said in a statement.

Biden, a Democrat, served under President Barack Obama, who favored citizenship for millions of undocumented immigrants. But he also enforced the law, expanding family detention near the border and deporting a record number of immigrants, comparably more than Trump has so far.

Immigration normally resonates in Arizona, a border state that has long contended with migrant surges and internal battles about immigration crackdowns. But the once solidly Republican state is in play this year as it has shifted to the left, with the share of White voters shrinking and Latino voters on the rise.

Polls show that Biden has an edge over Trump in Arizona, which the president won by less than 4 points four years ago. The coronavirus also has shifted the political calculus in a state where nearly 1 in 5 residents are age 65 or older, a high-risk group.

Arizonans were hammered by the coronavirus earlier this year and nearly 6,000 people have died. After an aggressive campaign to drive down the infections, Gov. Doug Ducey (R), a Trump supporter, and health officials were warning residents Thursday about a recent uptick in infections.

“We are concerned and we’re watching what is happening in Arizona, as well as what is going on nationally,” Cara Christ, director of the Arizona Department of Health Services, told local media.

Wolf did not acknowledge those concerns in his speech, and has instead attempted to spotlight the threat of the virus outside U.S. borders, even though the total number of reported cases in the United States is by far the highest in the world.

In his speech, Wolf said the Trump administration effectively closed borders and limited illegal immigration to mitigate the spread. He said that “experts predict an increasing number of aliens will journey to our borders in the near future as a result of the devastation the covid-19 pandemic has brought to Latin America,” which could lead to a “public health crisis.”

Advocates for immigrants and the environment slammed Wolf’s appearance, saying it was a political move.

“It’s pathetic to see Wolf making a fool of himself shilling for Trump,” said Laiken Jordahl, of the Center for Biological Diversity Action Fund, which has accused the Trump administration of bulldozing sacred lands to make room for the president’s border wall. “He’s not welcome here.”

Wolf spoke in Phoenix four years after Trump delivered a signature immigration speech in August 2016, months before he was elected.

Back then, Trump mocked candidate Hillary Clinton for worrying about separating families through deportation, vowed to build “a great wall” on the southern border at Mexico’s expense, and said he would stop admitting migrants who enter the country illegally.

Aided by the pandemic, Trump has sharply reduced travel to the United States.

But he did not fulfill many of those early promises: Mexico has not paid for the wall, deportations are far lower than they were under Obama, and a record number of migrant families and unaccompanied minors, mostly from Central America, surged across the border in fiscal 2019 because the Trump administration could not detain them or process their cases quickly enough, according to the Congressional Research Service.

Wolf also highlighted worries about “evil people” who want to harm Americans including law enforcement.

He highlighted the case of an immigrant from El Salvador, in the United States illegally, with a criminal record, who on Tuesday allegedly shot and killed Houston Police Sgt. Harold Preston, 65. The police commander was weeks away from retiring. Another officer, Courtney Waller, was injured in the exchange of gunfire during a domestic disturbance call.

“This tragedy should have never happened, and I, along with the men and women of the department, will continue to fight to stop these senseless acts of violence,” Wolf said.