Washington (CNN) Donald Trump's colorful presidential campaign heads to the U.S.-Mexico border on Thursday, where the billionaire businessman is sure to expand on his controversial comments about immigrants.

He'll travel to Laredo, Texas, for a tour with U.S. border patrol agents.

The trip comes as Trump dominates the Republican presidential contest -- both in the polls and in the headlines. He sparked a fierce debate among Republicans last month when he referred broadly to Mexican immigrants as criminals and rapists . He angered many Republicans this weekend by questioning John McCain's status as a war hero. And on Tuesday, he escalated a verbal war with Lindsey Graham by releasing the South Carolina senator's cell phone number.

A chapter of the National Border Patrol Council, the agency's union, invited Trump earlier this month to tour one of the most active parts of the border with the agents who work there. Hector Garza, the president of the chapter, told CNN earlier this month that he wanted "to give Donald Trump a state of the border" and a "boots on the ground perspective."

Garza, a border patrol agent, said his invitation was not an endorsement of Trump's presidential run, saying that his group regularly invites politicians -- including previous tours with GOP Reps. Jason Chaffetz of Utah and Blake Farenthold of Texas.

He also invited Sen. Ted Cruz, who is also vying for the Republican presidential nomination, last month.

Garza said his organization's only goal is to encourage policies that will lead to a strong border and a safer environment for his fellow agents. The Laredo chapter is one of the largest in the country, Garza said, representing about 1,400 border patrol agents.

While he would not comment on Trump's controversial remarks about Mexican immigrants, Garza said agents posted near Laredo "do see a lot of aliens with a criminal history," and said that while not all are criminals, a "large number" have criminal backgrounds.

Trump first told CNN he had been invited to the border by a group of border patrol agents during a phone interview two weeks ago. The visit will be Trump's fourth to the border, by his count.

"I'm the only one that speaks their language," he said.