Democratic U.S. Senate candidate Zak Ringelstein, who this week canceled a campaign tour of Maine to travel to the U.S.-Mexico border, was arrested Friday for refusing to leave a child detention center in Texas after being told he would not be allowed inside.

“Zak is now a political prisoner of the Trump regime,” read a tweet from Ringelstein’s campaign account.

It’s not clear what Ringelstein was arrested for, but he had announced on Wednesday that he was traveling to McAllen, Texas to bring supplies to children separated from their parents under President Trump’s zero-tolerance policy regarding people who cross the border illegally. Under mounting pressure from both Democrats and Republicans, Trump signed an executive order temporarily ending the separation policy.

Ringelstein’s campaign said he planned to “deliver water, food, blankets, books, and toys to the children imprisoned there,” but it appears he was turned away on Friday and then arrested after he didn’t leave. He was arrested after persistently asking authorities to be let into a detention facility and the confrontation was broadcast on his campaign’s Facebook page.

The 31-year-old New Hampshire native announced in February that he would challenge independent U.S. Sen. Angus King for one of Maine’s two Senate seats. Republican Eric Brakey also is in the race.

Ringelstein is a former teacher and aspiring country music singer who moved to Maine two years ago.