Kamala Harris was due to deliver a tough-on-illegal-migration message after visiting the US-Mexico border Friday, directly tackling the politically explosive issue in a bid to blunt one of Donald Trump's main attack lines in their fight for the White House.
The US vice president's trip to Arizona -- her first to the border since replacing President Joe Biden as Democratic nominee in July -- comes as polls show illegal migration remains one of her biggest vulnerabilities against the Republican.
Harris will call for tougher security in the speech in the border town of Douglas and accuse Trump of killing attempts to pass a bipartisan migration bill in hopes of boosting his own election chances, her campaign said.
"The American people deserve a president who cares more about border security than playing political games," she plans to say, according to her campaign.
A campaign official told reporters that Harris will announce that as president she would strengthen border restrictions recently put in place that successfully stemmed the flow of undocumented crossings.
Harris made an unannounced visit to the border wall in Douglas, where she met with Border Patrol officials and was photographed alongside the distinctive metal slats at the international frontier.
Arizona is also one of the half-dozen battleground states that are expected to decide the agonizingly close November 5 election, and it is where polls show Harris may have to do the most work.
Former president Trump has turbocharged the border issue in recent weeks as he seeks an edge against Harris, America's first female, Black and South Asian vice president.
The 78-year-old has called for mass deportations, amplified bogus claims about migrants eating pet cats and dogs, and stepped up his racially charged rhetoric about an "invasion" of illegal immigrants who he claims consist of murderers, rapists and mentally ill people.
Hours before Harris was to speak in Arizona figures from the US Department of Homeland Security showed 425,000 non-citizens convicted of crimes are living in the United States, including more than 13,000 who have convictions for homicide.
Trump leapt on the news, claiming these people had been "let out of jail, and they're roaming our streets."
Trump claimed -- erroneously -- that the numbers referred to people who had illegally crossed the border under the Biden-Harris administration.
In fact, the figures give no details on how long any of these people have been in the United States, and experts say many of them could have been in the country for decades.
"These are people who, primarily, have already been charged and convicted and served their time," Aaron Reichlin-Melnick of the American Immigration Council told AFP.
Reichlin-Melnick added that, under Trump, there were millions of non-citizens living in the United States, including hundreds of thousands with criminal records.
"The only reason that they cannot be deported is because of diplomatic issues with their home country and nothing to do with the US government's policy or practices," he said.
Recent polls have seen Harris eating into Trump's lead on migration with voters, yet it still remains a weak spot, with record numbers of illegal border crossings under her and Biden's watch.
But Harris points to the fact that numbers have plummeted since Biden signed an executive order in June temporarily closing the border to asylum seekers -- to around 58,000 in August from a peak of 250,000 last December.
Republicans have also focused on Harris's role early in the Biden administration when the president tasked her with looking into the causes of illegal migration from Central America -- falsely calling her a "border czar" and implying that she had overall control over US border policy.
Trump has meanwhile doubled down on his divisive rhetoric targeting migrants, with the billionaire seeing it as appealing to his base of largely white, blue-collar voters.
In his remarks on Thursday, Trump also repeated his claim that migrants were "infecting our country," using language that Biden's team has previously compared to that used by Nazi Germany.
Trump and his running mate J.D. Vance have in recent weeks played up false stories about Haitian migrants eating pets in the town of Springfield, Ohio.
