Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeRepublican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style Bush endorsing Biden? Don't hold your breath MORE (R-Ariz.) on Tuesday mocked former Arizona county Sheriff Joe Arpaio's bid to run for his Senate seat.

“Write about it fast because it won’t last long,” Flake told reporters at the Capitol.

Arpaio announced Tuesday he will run for Senate to replace Flake, who announced last year he will not seek reelection.

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Arpaio gained popularity among immigration hard-liners during his time as Maricopa County sheriff, proudly calling himself “America’s toughest sheriff” and touting a strict approach to border security.

President Trump last year pardoned Arpaio after he was convicted of ignoring a court order related to racial profiling in his division.

Arpaio said he plans to run for Senate “to support the agenda and policies of President Donald Trump.”

Flake has been a frequent critic of Trump, earning the president’s ire on Twitter.

In a floor speech in October announcing his plans to retire, Flake blasted the president and said fellow Republicans had abandoned their principles.

Last month, Flake said the crowds at rallies for Trump and other Republicans reflect “spasms of a dying party,” and that the GOP needed a governing agenda to reach more voters.

Last year, one of Flake's sons filed a malicious prosecution lawsuit against Arpaio, claiming Arpaio pursued felony animal cruelty charges against him and his then-wife in an effort to hurt his father politically.

Flake's son ultimately lost the civil lawsuit against Arpaio.

This story was updated at 3:50 p.m.