Arizona Republican Joe Arpaio, the former Maricopa County sheriff who became famous for his controversial stance on immigration, has announced his candidacy for the U.S. Senate, saying he wants to join Congress so he can help President Trump.Arpaio, who will turn 86 in June, made the announcement in a tweet on Tuesday, contending helping Trump was his "one unwavering reason" for running.Arpaio is running for the seat being vacated by Sen. Jeff Flake, a fellow Republican who has been a critic of Trump — and who announced last October that he would not seek re-election.The former sheriff announced his plan to run for the Senate less than a year after he was convicted of criminal contempt — a crime for which Trump pardoned Arpaio in August, after holding a rally in Phoenix.Arpaio told NBC News that he didn't tell Trump about his decision ahead of time — and that he's running because Washington needs "fresh blood."In announcing his candidacy, Arpaio joins at least one Republican rival. As member station KJZZ reports, former state Sen. Kelli Ward has already launched her campaign, and Rep. Martha McSally has also "hinted" at running for Flake's seat.This year's midterm elections are being held two years after Arpaio lost his sheriff's job to Democrat Paul Penzone, a former sergeant in the Phoenix police department. Arpaio, who had held the office for 24 years, lost despite amassing more than $12 million in campaign funds.Arpaio's entry into the Senate race prompted immediate criticism from Democratic National Committee Chair Tom Perez, who released a statement saying, "Joe Arpaio is one of our nation's most notorious agents of racism and bigotry. He has spent his career tearing apart immigrant families and devastating Latino communities, and he has no place in the U.S. Senate."Famous for embracing the title of "America's Toughest Sheriff," Arpaio was convicted by a federal judge after the Maricopa lawman defied an order to stop detaining immigrants simply because of their legal status. His deputies maintained that practice for 18 months after a court told Arpaio to stop targeting Latino drivers.The misdemeanor criminal conviction had carried a maximum sentence of six months in jail and a fine. But Arpaio was pardoned before his sentencing date arrived in October.Arizona will hold its primary in late August, with the midterm election scheduled for Nov. 6. Copyright 2018 NPR. To see more, visit http://www.npr.org/.