Donald Trump brought his anti-immigration rhetoric to the busiest border crossing between the U.S. and Mexico on Friday, May 27, resulting in one of the largest demonstrations thus far organized against him and the arrests of at least three dozen protesters.

Throngs of marchers convened outside the San Diego Convention Center to raise their voices to the presumptive Republican nominee, who has vowed to deport millions of immigrants if he is elected.

"We're going to build a wall," Trump told supporters gathered inside the venue, leading to a flood of skirmishes erupting near the arena.

Police Intervene

Police brought out their batons when some protesters tried to climb into a secure area where officers were monitoring the situation. Just last month, protesters burned an American flag and an effigy of Trump at another California rally held for him.

"I don't agree with a lot of things that the presidential candidate Donald Trump has put out there," said protester Judith Castro. "Like the fact that he's using racism, discrimination."

As the rally ended, police swarmed the area in riot gear, warning people they were part of an unlawful assembly and that everyone who remained there illegally and was subject to arrest.

Inside, Trump boomed, "Honestly, folks, we have leadership right now in this country, especially at the top, that is grossly incompetent. They don't know what the hell they're doing."

Trump Vows to Deport Millions

Besides vowing to deport millions, Trump has also pledged to build a wall along the southern border to further keep immigrants out that he insists Mexico would be forced to pay for. Trump's plan entails forcing Mexico to foot the bill for the wall by threatening to cut off the flow of billions of dollars in payments that immigrants regularly send home to loved ones.

By contrast, Democratic front-runner Hillary Clinton has committed to a plan of immigration reform.