Jon Tester (MT):

Jon Tester has been serving as a Senator from Montana 2007. Prior to serving in the Senate, Tester was a member of the Montana Senate and a music teacher. As a Senator, Tester has focused on issues such as veterans’ affairs, agriculture, and healthcare. He is known for being a moderate within the Democratic Party and has often been willing to work with Republicans on legislation, which like Sen. Machin and Sen. Sinema, has somewhat made him an outcast from the Democratic party.

Tester is also the lone Democrat in a deep red area, like Manchin. While Tester stated that he believes that he’d win a fourth term if he runs, he hasn’t stated whether or not he’ll be running.

According to Ellis Insight:

Sen. Tester is beginning to appear on more potential retirement lists, as he did in the Fox News story.  Montana, like West Virginia, is another state that is turning solidly Republican making Sen. Tester’s re-election less than a sure thing.  The last time he was on the ballot (2018) he defeated current US Congressman Matt Rosendale (R-Glendive) by only a 50-47% margin in a state that has only grown more conservative since that time.  In the 2020 election, Republican candidates won all eight of Montana’s statewide elections with victory margins between nine and 19 percentage points.  During the same period, Sen. Tester’s voting record has moved decidedly to the left where he can no longer be considered a centrist incumbent.

Additionally, Montana’s other Senator, Republican Steve Daines, is now chairman of the National Republican Senatorial Committee (NRSC) thus guaranteeing that Montana will be a top national GOP target with heavy funding to support the party’s eventual nominee.  Therefore, with obvious lucrative opportunities available to Sen. Tester in the private sector, he might decide his future is more appealing on the outside of elective politics than fighting what will likely be a more difficult re-election campaign than he has before experienced.