Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Joe Arpaio — the controversial sheriff beloved by immigration hard-liners who was pardoned of criminal contempt charges by President Donald Trump last year — announced Tuesday he will run for U.S. Senate in Arizona.

"I am running for the U.S. Senate from the Great State of Arizona, for one unwavering reason: to support the agenda and policies of President Donald Trump in his mission to Make America Great Again," Arpaio tweeted.

Arpaio told NBC News that Washington needed "fresh blood" and that he hadn’t informed Trump of his decision to mount a Senate bid.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

The 85-year-old former sheriff is running for the seat being vacated by Sen. Jeff Flake, who announced in October he would not run for re-election, citing his dismay with Trump and the direction of the Republican Party.

Arpaio served as sheriff of Maricopa County, which includes Phoenix, for 24 years before losing his re-election bid last November. He is known for controversial policies — including jailing prisoners in a tent city and forcing detainees to wear pink underwear — that made him popular with some on the right.

He was a devoted supporter of Trump during the 2016 campaign, and in August received a presidential pardon for a criminal contempt conviction stemming from his decision to ignore a judge's order not to detain suspected undocumented immigrants.

In July, a U.S. District judge had found Arpaio guilty of misdemeanor contempt of court for willfully violating a 2013 order from another federal judge to end the immigration arrests on suspicion. The district judge said in 2013 that Arpaio and his deputies had engaged in racial profiling against Latinos, backing up the findings of a Justice Department report several years earlier.

White House Press Secretary Sarah Huckabee Sanders declined to weigh in on Arpaio's candidacy during a briefing with reporters Tuesday.

Arpaio will face tough competition in the GOP primary for the seat from former state Sen. Kelli Ward, a firebrand conservative who had received the backing of former Trump strategist Steve Bannon.

Rep. Martha McSally, R-Ariz., is also said to be eyeing a run for the seat. Two sources familiar with McSally’s decision say the Arizona Republican congresswoman will officially announce her Senate campaign on Friday.According to The Arizona Republic, she told her House colleagues in November that she was planning on entering the race.