Donald Trump went after Jeb Bush this morning ahead of the former Florida governor's visit to the Mexican border.

Trump predicted that Bush will find out, contrary to what he said last year, that those who cross the border are not doing so as an "act of love."

"It's great that he's going to the border. He'll now find out it is not an act of love. ... It's rough, tough stuff. This is not love. This is other things going on," said Trump, who recently took a trip to the border.

He noted that illegal immigrants are bringing in drugs, while Mexico brings in "billions" in drug money out of the United States.

"We get the bad stuff, as usual, they get the good stuff," he said.

Trump said the candidates who have attacked him, like Rick Perry and Lindsey Graham, have since "gone down to zero" in the polls.

He pointed out that Bush has attacked him as well, in a "low-energy way," and is also dropping in the polls.

Trump also slammed Bush for the way in which he's financing his campaign.

"I know him. There's always strings attached with him. Many of the people who have given to Bush. They don't give because they like his hair color. They give for only one reason. Total strings attached. They want what they want," said Trump.

Trump said he turned down a $5 million offer from a lobbyist the other day because the money would have only come with "strings attached."

He said he recently got a long letter from a woman with a check for $7.32, while many others are sending him small amounts like 10 bucks. 

Trump said he'll only accept donations if there are "no strings attached." 

"The only string attached is I want to make America great again," he said. 

Watch the whole interview above, as Trump discusses the stock market plunge, Joe Biden and Hillary Clinton. 

Programming Alert: Bill O'Reilly interviews Donald Trump, tonight at 8/11p ET on "The O'Reilly Factor."