Donald Trump boarded his private jet for the Texas-Mexico border and flew headlong into fresh controversy as a border agents union announced it was boycotting his visit.
The real estate mogul and White House contender, who is streets ahead of his Republican rivals in some polls, is running an outspoken and aggressive campaign and has condemned illegal immigration.
"Getting ready to lift off for Laredo. Will land at 1:00 pm. Should be exciting and informative," he tweeted to his more than 3.3 million followers on Thursday (local time).
Trump's team say he will tour the town, visit the border, address local law enforcement and deliver a press conference.
But a border patrol union said it was boycotting the visit "after careful consideration of all the factors involved".
The League of United Latin American Citizens also announced that it would protest against Trump's arrival at Laredo airport. The town's population is 95.6 percent Hispanic or Latino.
"Make no mistake, our border with Mexico is not secure and there's no doubt that we need to have an honest discussion about that," the National Border Patrol Council said.
"Our intention to meet with Mr Trump was to provide a 'boots on the ground' perspective to not only Mr Trump, but to the media that would be in attendance at this event," it said.
But it added that the local branch of the union "does not endorse candidates for any political office".
Trump issued a rapid-fire response, claiming the union had been silenced by superiors in Washington DC "who do not want people to know bad it is on the border".
The visit would continue "despite the great danger" he said in a statement, alleging that union members "are being silenced, and are very unhappy about it".