Donald Trump took his presidential campaign down to the border with Mexico on Sunday, doubling down on the hardline immigration rhetoric that was a hallmark of his first White House term.

The Republican leader asserted that border security had evaporated under President Joe Biden, with "gangs of thugs" pouring into the US.

"We're going to take over that border and we're going to make it the most secure border in our history," Trump said.

He was speaking to a supportive group of border guards and Texas Governor Greg Abbott, a like-minded Republican who has endorsed Trump's 2024 campaign.

In recent weeks, the former president has ramped up his campaign rhetoric to extreme levels, warning that undocumented migrants are "poisoning the blood of our country" and denouncing his political opponents as "vermin."

'The enemy'

He employed similar language Sunday, referring to some migrants as "the enemy" and predicting that 15 million undocumented migrants would be in the country by the end of Biden's first term -- a number millions larger than estimates by most non-governmental groups.

Abbott, like Trump, has pursued hard-line immigration policies, including installing a 1,000-foot (330-meter) floating barrier in the Rio Grande that critics say imperils migrants attempting to cross.

The Texas legislature recently passed a bill that would make entry into the state without papers a crime punishable by up to two years in jail.

The bill would also allow Texas officers to arrest anyone they believed was in the state without proper documentation, a power that critics say is sure to be abused.

Abbott has vowed to sign the measure into law.

The Trump campaign has made clear that if the real estate tycoon returns to the White House, he will engineer a tough crackdown on the undocumented, reportedly including huge detention camps and mass deportations.

'Radically anti-immigrant'

Texas has been a reliably conservative bastion for Trump as he looks forward to the 2024 elections, and he holds huge leads both there and nationwide over his Republican rivals.

Trump and Abbott blame Biden for the current migrant crisis, as thousands of people flow into the country from Latin American countries beset by crime, poverty and violence.

How Biden handles the crisis could play a major role in the 2024 election.

The president met Friday with Mexican President Andres Manuel Lopez Obrador on the sidelines of the Asia Pacific Economic Cooperation forum in San Francisco, and thanked the Mexican leader for his "cooperation" over the migrant crisis.

Lopez Obrador, in turn, thanked Biden for being the first recent president "who has not built walls."

But the Mexican leader blasted the Texas border bill, saying it would lead to family separation, discrimination and racial profiling.

Rights groups have also sharply assailed the bill.

If enacted, the measure would be among the "most radical anti-immigrant bills ever passed by any state," said Oni Blair, who heads the American Civil Liberties Union's Texas chapter.