Montana Lt. Gov. John Walsh, a Democrat, was appointed Friday to fill the unexpired term of longtime Democratic Sen. Max Baucus, who is leaving the Senate to serve as U.S. ambassador to China.

Walsh, 53, was already an announced candidate for the seat Baucus had planned to vacate at the end of this year. His appointment by Democratic Gov. Steve Bullock gives the former adjutant general of the Montana National Guard a leg up in the November contest to replace the six-term senator.

Friday's announcement sets up what's expected to be a pitched and costly battle crucial to GOP hopes of taking over the Senate — hopes that are contingent on winning red state seats now held by Democrats.

Baucus, the chairman of the powerful Senate Finance Committee, revealed last April that he would retire this year at the end of his term; his plans were upended in December when President Obama tapped him for the ambassadorship.

He was unanimously confirmed Thursday by his Senate colleagues.

"I wanted to appoint someone who I believed would represent the values Montanans hold important," Bullock said in announcing the appointment of Walsh, his 2012 running mate. "I wanted to appoint someone who I believed would be working to find solutions, not further dividing our state and nation. And I wanted to appoint someone who I truly believed would wake up each day focused on putting Montana – and Montanans – first."

Walsh emerged as the frontrunner to replace Baucus after popular former Democratic Gov. Brian Schweitzer, widely expected to seek the Senate seat, declined to run.

Schweitzer was initially seen as the Democrats' strongest candidate to retain the Senate seat in a state where just 41 percent of the electorate voted for Obama in 2012. Montana voters are not entirely predictable: that same year incumbent Democratic Sen. Jon Tester won re-election with more than 48 percent of the vote.

Walsh, an Iraq War combat veteran, is considered a strong candidate but does not have the same cache with voters. He also could face two primary opponents. Former Lt. Gov. John Bohlinger and rancher Dirk Adams have thrown their hats in the race, though Walsh's appointment clouds their path.

"Lieutenant Governor John Walsh has spent his life serving his state and his country," said Colorado Sen. Michael Bennet, chairman of the Democratic Senatorial Campaign Committee. "John is the kind of guy who may not agree with the party on every single issue, but he has the selflessness and courage to always do what he thinks is right for Montana, and that is exactly the kind of leadership we need here in the U.S. Senate."

The Republican frontrunner for Baucus' seat, freshman U.S. Rep. Steve Daines, this week launched his first television ad – a biographical spot that focuses on his business experience. A former executive with a Bozeman-based cloud-hosting software company that's part of the Oracle Corporation, Daines reported having $1.9 million in his campaign account, according to theBillings Gazette. Walsh reported a balance of $435,000 in his account.

State Rep. Champ Edmunds and air traffic controller David Leaser are also running for the Republican nomination.

Republicans in recent months had already begun focusing on Walsh, highlighting an Army reprimand he received in 2010. Walsh was found to have used his National Guard position to strong arm subordinates into joining a private guard lobbying group in which he was seeking a leadership position.

Walsh disputed the finding, and then-Gov. Schweitzer wrote a letter supporting him. Walsh resigned his post to run for lieutenant governor in 2012.

Both the Cook Political Report, and the Rothenberg Political Report, non-partisan analysts of elections and campaigns, rate the Montana race a toss-up.

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