HELENA — Lt. Gov. Mike Cooney is announcing Wednesday that he’ll run for governor in 2020, becoming the third and most prominent Democrat to enter the crowded battle for an open governor’s seat.

Cooney, 64, will make his announcement in his hometown of Butte.

Cooney is a veteran of five statewide campaigns during his lengthy career, winning the post of secretary of state in 1988, 1992 and 1996 and then lieutenant governor in 2016, with running mate Gov. Steve Bullock.

Bullock, who’s running for president, cannot run for a third term as governor because of term limits.

The only statewide campaign Cooney has lost was in 2000, for governor, when he came in last in a three-way Democratic primary won by Mark O’Keefe, who went on to lose against Republican Judy Martz.

Cooney will be involved in another primary battle this campaign, but against lesser-known candidates: House Minority Leader Casey Schreiner of Great Falls and former state lawmaker Reilly Neill of Livingston.

The winner will try to keep the governor’s chair in the Democratic column, where it’s been for the past 16 years.

Montana Republicans are eager to win back the governorship, and three prominent Republicans are in the race: Attorney General Tim Fox, U.S. Rep. Greg Gianforte and state Sen. Al Olszewski of Kalispell.

Cooney is Bullock’s third lieutenant governor, appointed in late 2015 after then-Lt. Gov. Angela McLean quit to take a job with the state university system.

Cooney has been involved in Montana politics since the early 1970s, when he worked on Max Baucus’s first run for the U.S. House. He was a state representative at age 23, from Butte, and won the office of secretary of state in 1988, twice winning re-election.

He also served as a state senator from Helena from 2003-2010.