Montana Gov. Steve Bullock Steve BullockSenate Democrats demand White House fire controversial head of public lands agency Pence seeks to boost Daines in critical Montana Senate race Trump's fear and loathing of voting by mail in the age of COVID MORE (D) formally announced his 2020 Senate run on Monday, tweeting his first campaign ad.

“I've always fought for the people of Montana. Together, we expanded health care, protected public lands, banned dark money in politics & more,” Bullock tweeted. “Now I'm taking that fight to the US Senate. Let’s make Washington work more like Montana.”

In the ad, Bullock touts his record as governor, including actions to protect public lands, the nation’s sixth-fastest weekly wage growth, the creation of 34,000 jobs and a freeze on college tuition.

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I've always fought for the people of Montana. Together, we expanded health care, protected public lands, banned dark money in politics & more. Now I'm taking that fight to the US Senate. Let’s make Washington work more like Montana. Join us: https://t.co/vyPPioB0tJ #MTSen #MTpol pic.twitter.com/6VuCKsNTeW — Steve Bullock (@stevebullockmt) March 9, 2020

The governor, who will challenge Sen. Steve Daines Steven (Steve) David DainesSenate Democrats demand White House fire controversial head of public lands agency Pence seeks to boost Daines in critical Montana Senate race The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support MORE (R), announced his run on the filing deadline.

Bullock, who had initially said he would finish his term as governor as recently as February, reportedly decided on a run after appeals from Senate Minority Leader Charles Schumer Chuck SchumerMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt Schumer lashes out at Trump over 'blue states' remark: 'What a disgrace' MORE (D-N.Y.) and former President Obama.

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Bullock joins former Colorado Gov. John Hickenlooper John HickenlooperGOP campaign director: 'There's no doubt that Republicans will control the Senate' Susan Collins challenger open to nixing Senate filibuster Democrats struggle to harness enthusiasm of Gen Z voters MORE as the second former Democratic presidential candidate who will mount a Senate run after exiting the presidential race.

Bullock entered the then-crowded presidential field in May, making the stage for a single debate and frequently touting his ability to win as a Democrat in a state that went heavily for President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE in 2016.

He dropped out of the 2020 presidential race in December.

"Steve Bullock ran his administration like a frat house and acquiesced to the far left during his comical presidential run, not exactly the strongest way to launch a Senate campaign," National Republican Senatorial Committee spokesman Nathan Brand said in a statement.

"Bullock supported impeaching President Trump, wants to ban guns, and ignore illegal immigration. One can see why, given their visceral disdain for the Montana way of life, Washington Democrats rolled out the red carpet for Bullock," Brand added. "Meanwhile, Steve Daines always puts Montana first, is a proven leader and a strong ally for President Trump."

Updated at 9:19 a.m.