For nearly four years, the United States is experiencing its worst border crisis in the history of the world, Republican presidential candidate and former president Donald Trump said.

The remarks by Trump on Thursday came on the eve of his Democratic rival Vice President Kamala Harris's visit to the US-Mexico border down South on Friday.

“For nearly four years, we have been living through the worst border crisis in the history of the world. There's never been anything like it, which has brought untold suffering, misery, and death upon our land. The architect of this destruction is Kamala Harris,” Trump told reporters at a news conference in New York.

“When you look at the four years that have taken place after being named border czar, Kamala Harris tomorrow (Friday) will be visiting the southern border that she has completely destroyed. Why would she go to the border now, playing right into the hand of her opponent. There can be no justification for what she's done. Nobody is saying, oh, gee, she's done a fabulous job. She's done the worst job probably in the history of any border, not just our border. She keeps talking about how she supposedly wants to fix the border,” Trump said.

“We would merely ask, why didn't she do it four years ago? She's got no plans, got no talent, got no ability to do it. I'm here today to present you with the facts and only the facts about how comrade Kamala Harris willfully threw open our border, helping to virtually destroy our country. Our country has never been under siege like this,” Trump said.

Four years ago, he said, Harris inherited the most secure border in US history with the lowest illegal immigration on record.

“Those who violated our borders were captured, detained, and quickly sent back home under the Trump administration,” he said.

“But on her first day in office, Kamala Harris terminated every single Trump policy that sealed and secured the border. She ordered an immediate stop to the completion of the border wall. It was almost complete. We built hundreds and hundreds of miles of wall, and it worked. She suspended all deportations. She instituted catch and release across the entire southern border,” Trump alleged.

“She sent Congress a bill demanding amnesty for all illegal aliens, every single illegal alien, even if they're criminals, murderers, drug dealers, human traffickers. She wanted amnesty for everybody. This is a radical left person,” he said.

Meanwhile, at an election rally in Pennsylvania, Harris told her supporters that Trump was an unserious man.

“Donald Trump has a very different plan based on a very different vision of who we are and the needs of the American people. I’ve said this before and I’ll say it again. In many ways, Donald Trump is an unserious man. The consequences of putting him back in the White House are extremely serious,” she said.

“Look, for example, at Project 2025, a detailed and dangerous blueprint for what he will do if elected president again. He intends to cut social security and Medicare; repeal our climate investments and send thousands of good-paying clean energy jobs overseas; and he wants to impose what I call a Trump sales tax, a 20 per cent tax on everyday necessities, which will cost the average American family an additional USD 4,000 a year,” Harris said.

Trump is headed to Michigan on Friday to speak on manufacturing.

“Donald Trump is one of the biggest losers of manufacturing in American history. He makes empty promises after empty promises to American workers but never delivers. As President, he cut taxes for corporations, encouraged outsourcing, and lost nearly 200,000 manufacturing jobs, including auto jobs. He has joked about firing workers, supported state anti-union laws, and suggested companies move jobs out of Michigan,” Harris alleged on Thursday night.

“Enough is enough. American workers deserve a leader who keeps their promises and stands with workers when it matters, and as President, I will bring autoworker jobs back to this country and create an economy that strengthens manufacturing and unions and builds prosperity and security for America’s future. I will always stand with the UAW. Trusting Donald Trump again is a risk America's autoworkers cannot afford,” she said.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.