US President Joe Biden and Donald Trump will pay dueling visits to the US-Mexico border Thursday in a bid to win over voters on one of the most divisive issues of November's presidential election.
The showdown in Texas comes at a time when record numbers of migrant crossings into the United States are posing a major threat to Biden's chances of preventing a Trump comeback.
Democrat Biden will meet border patrol and other law enforcement agents in Brownsville, Texas, while Republican Trump heads to Eagle Pass, about 300 miles (480 kilometers) to the west.
Biden has sought to defuse the politically toxic border issue by blaming Republicans in Congress for failing to back an immigration reform package negotiated over months by both parties.
White House Press Secretary Karine Jean-Pierre said Thursday that Biden would deliver remarks in Brownsville to highlight "what he has done to continue moving forward in dealing with this issue and how Republicans have gotten in the way."
The bipartisan bill, she said on CNN, had even won the support of typically conservative groups such as the Border Patrol Union and US Chamber of Commerce.
"In this political time, it is unreal, unheard of, to see that type of support for a bipartisan bill."
But for Trump, a hardline anti-immigration stance has been central to his political identity for years, and he has pledged the biggest ever US deportation program if he returns to the White House.
"No country can sustain what is happening to our country," the former president told the Conservative Political Action Conference (CPAC) in Washington earlier this month.
Trump claimed migrants were "killing our people, they're killing our country" -- echoing the increasingly far-right rhetoric that saw him describe migrants last year as "poisoning the blood" of the United States.
The split-screen moment less than eight months before Americans go to the polls highlights the high stakes of the border issue as Biden, 81, and Trump, 77, head for a likely election rematch.
Biden insisted earlier this week that he hadn't deliberately planned the clash of schedules with bitter rival Trump, whose rhetoric the Democrat has likened to that of the Nazis.
"I planned for Thursday. What I didn't know was that my good friend apparently is going," he told reporters during a visit to an ice cream shop in New York.
Biden also declined to say whether he would meet with migrants, after criticism that he did not do so on a previous visit.
Republicans blame Biden's policies favoring the right to asylum for the flow of migrants, while the White House says that Trump's party is deliberately sabotaging a bipartisan attempt to find a solution.
A $20-billion immigration package -- which included reforms widely seen as the most strict in decades -- failed to pass the Senate in early February.
"Republicans rejected it. Why did they do that? They did that at the behest of the former president, Donald Trump, who asked them to not take it up... for his own political gain," Jean-Pierre said Thursday.
The border issue has also become tangled up in a bitter row over US aid for Ukraine's fight against the Russian invasion, with Republicans insisting migration must be tackled before they unblock funding for Kyiv.
Public concern about illegal immigration is higher under Biden than it was under the last two administrations, with a majority now supporting a border wall of the kind Trump started building, according to a new poll by Monmouth.
A poll by US broadcaster NBC in February showed Trump leading Biden by 30 points on the issue of immigration.
