Trump claims immigrants are illegally flooding into America 'so they can go and vote'
Donald Trump speaking at the 2014 Conservative Political Action Conference (CPAC) in National Harbor, Maryland (Gage Skidmore/Flickr)

Republican presidential candidate Donald Trump said on Friday that U.S. officials were allowing illegal immigrants into the United States so they can vote, returning to a core issue as he girded for a crucial second debate against Democrat Hillary Clinton.

"They're letting people pour into the country so they can go and vote," Trump said during a meeting with representatives of the National Border Patrol Council, the union that represents Border Patrol agents, at Trump Tower in New York.

Trump provided no specifics on the accusation.

The New York businessman's comment came ahead of his second presidential debate on Sunday night against Clinton, a town hall-style event at which he must do well as he tries to rebound from a slump in some polls after a rocky first debate late last month.

Clinton has been quietly immersed in debate preparation with top aides since her last campaign event on Tuesday.

The U.S. presidential race, which has commanded Americans' attention all year, has abruptly taken a backseat as the focus has shifted to Hurricane Matthew's slow, destructive march up the eastern coast of Florida.

Slowing illegal immigration has been a signature policy theme for Trump, who has vowed to build a wall along the U.S. southern border with Mexico.

While Democratic President Barack Obama has struggled with controlling the flow of illegal immigrants across the southern border, there has been no evidence that U.S. officials are purposely allowing them to cast ballots in American elections.

In order to register to vote, Americans must provide proof of citizenship, documentation that illegal immigrants would not have unless obtained illegally.

Trump praised the Border Patrol agents, saying they love their country and want to protect its borders.

"It's much easier if you don't do this. It's much easier if you just let people come in," Trump told them. "But you love our country. You know it's wrong."

Trump's comments about people coming across the border to vote were a response to Art Del Cueto, president of the union's Tucson, Arizona, chapter.

Del Cueto said people who were apprehended crossing the border illegally and who have criminal records were not being dealt with because immigration authorities were tied up helping people get citizenship.

Trump asked why, and del Cueto responded, "so they can go ahead and vote before the election."

"They want to hurry up and fast-track them so they can go ahead and be able to vote for the election," Del Cueto said a few moments later, without providing specifics.

"You hear a thing like that, it's a disgrace," Trump said.

(Reporting by Emily Stephenson; Writing by Steve Holland; Editing by Jonathan Oatis)