Washington (CNN) Joe Arpaio, the Republican former Maricopa County sheriff known for his hard-line immigration tactics, says he's running for Senate.

Rep. Martha McSally, the preference of national Republicans in the race to replace retiring Republican Jeff Flake, is also set to enter the race this week. And conservative Kelli Ward is already in the race -- setting up another showdown between the establishment-backed candidate in McSally and anti-establishment forces after a similar battle cost the GOP a Senate seat in Alabama.

Flake predicted Arpaio's Senate run will be short-lived.

"Write about it fast cause it won't last long," he told reporters after an immigration-focused meeting at the White House.

"I have a lot to offer. I'm a big supporter of President Trump," Arpaio told the Washington Examiner in an interview kicking off his campaign. "I'm going to have to work hard; you don't take anything for granted. But I would not being doing this if I thought that I could not win. I'm not here to get my name in the paper, I get that every day, anyway."

Arpaio was defeated in the 2016 election after 24 years in office as sheriff. He was convicted last year of criminal contempt for defying a court order to stop racially profiling Latinos but was pardoned by President Donald Trump, whose presidential campaign Arpaio had supported, in August before serving any jail time.

Arpaio told supporters in a fundraising email that he'd filed the paperwork to run in Arizona's late-August Republican primary.

On Twitter , he said: "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."

Sets up primary fight

GOP Sen. Jeff Flake is retiring, setting up a fight among top Arizona Republicans for the nomination.

National Republicans have landed their top recruit for the seat: Rep. Martha McSally is set to holds events Friday in Tucson, Phoenix and Prescott where she'll make what's being billed as a "special announcement." Two Republicans familiar with McSally's plans say she'll announce she's entering the race.

Arpaio and McSally would join Kelli Ward, the conservative state senator who drew 40% of the vote in the 2016 primary against Sen. John McCain, in the race.

Ward is supported by a super PAC funded by the GOP megadonor Mercer family. She was also backed by Steve Bannon -- though Ward distanced herself from the former White House chief strategist after Bannon's comments in a new book drew condemnation from Trump.

Though the primary is months away, it bears some similarities to the three-way Republican primary ahead of the Alabama special election in December. Arpaio, like Roy Moore, is a controversial figure with a solid base of die-hard suporters. Ward, like Rep. Mo Brooks, is also well-liked by anti-establishment conservatives. And McSally, like Luther Strange, is the establishment preference -- though Republicans argue McSally, a former fighter pilot who has proven her ability to raise money and win close races, is a stronger candidate.

A boost for Democrats

The Democratic candidate in a race that represents one of the party's best pick-up opportunities on the 2018 midterm map is Rep. Kyrsten Sinema.

Arpaio's entry into the race could be a boon for Arizona Democrats who will lean on Latino turnout in hopes of winning the Senate race.

Trump defeated Hillary Clinton by just 4 percentage points in Arizona in 2016, making it a much closer race than traditional swing states like Ohio, Iowa, Colorado and Virginia.

Latino voters made up 15% of the electorate and favored Clinton by a 2-to-1 margin, CNN's exit polls found.

Opposing Arpaio has long energized Arizona Democrats, and his presence in the race -- and pardon by Trump -- will be a fundraising tool for state and national Democrats.

Connecticut Sen. Chris Murphy immediately sent supporters a fundraising email seeking contributions to be split between his campaign account and Sinema's.

"Every Democratic voter should give a dollar to Arpaio's primary campaign because nobody energizes Latino voters nationally better than Joe Arpaio," said Rep. Luis Gutiérrez of Illinois, a retiring Democrat who is considering a 2020 presidential run. "He has 100% name recognition in the Latino community and will be enormously helpful to Democrats in Arizona and in every other Senate and House race in 2018 if he makes a serious run for the Senate."