But Baucus is different. Baucus has a special role in Montana politics, and it's not just because he's a fundraising juggernaut in a state that ranks in the bottom 10 states for personal income per capita.
"Whether you like him or you don't, you can't argue that when there's an important deal, healthcare trade, or taxes, Max Baucus is in the room," said Matt McKenna, who worked for Tester and is now a spokesperson for Bill Clinton. "Any time there's a late night press conference when they come out of the room, Max Baucus is always there. That is incredibly important to Montanans."
And there's more then just maintaining the Senate majority at stake for Baucus. Baucus aides like to say that the two senators are like brothers, with a bond as strong as any colleagues in the upper chamber. They hold weekly constituent meetings together, and consider one another strong advocates for their state.
"I saw Jon's tremendous commitment to Montana back in 2006, and over the last six years, I have seen him bring that same commitment to work every single day in the Senate," Baucus said in a statement. "Jon's record of delivering real results for Montana speaks louder than any campaign ad out there."
There's also a personal element to Baucus's involvement. For the most part Baucus has been able to win reelection with relative ease since coming to the Senate in 1978. One exception, however, was 1996.
It was an election that felt a lot like this year's in the Big Sky State. It was a two years after a GOP wave election, at was a presidential election year, and the guy running to defeat the vulnerable Democratic Senator from Montana was none other than Denny Rehberg.
Baucus was able to pull away at the end despite a bombardment of attacks from Rehberg and the National Republican Senatorial Committee hitting him for being a liberal and for voting for tax increases. During that election someone also leaked court documents relating to Baucus's divorce and issues with alimony.
"The 1996 race was a tough one," a Democratic lobbyist from Montana said. "There's still a little bit of bad blood from it. When you run against someone and it becomes personal you never really forget that."