In the waning days of a tumultuous legislative session in Montana’s Capitol, Carl Glimm, a state senator and a member of the ultraconservative Freedom Caucus, watched with exasperation as yet another Democratic-backed bill zoomed toward passage.

“Are we not embarrassed?” Mr. Glimm asked from the Senate floor in Helena. “This thing’s a big red ‘No,’ but I’ll tell you what — it’s going to be 23-27,” he added, predicting his own defeat. “Because, like we’ve said before, the cake is baked.”

In deep-red Montana, Republicans have controlled both houses of the Legislature since 2011, and the governor’s office since 2021. They ousted the last remaining Democratic statewide official, former Senator Jon Tester, in November.

Which has made it all the more aggravating for conservative lawmakers to find themselves effectively in the minority this year.

After an intraparty dispute in January, nine Republican state senators began breaking with their caucus on key votes, siding with the 18 Democrats in the 50-person chamber. The result: a 27-person majority that has all but locked Republican leaders out of power.

Some or all of the Nine, as the Republican defectors are known, have voted with Democrats to reauthorize a Medicaid expansion, establish a child tax credit, increase access to maternal health care and pass the state budget. They have helped block bills that would have weakened labor unions, made state judicial elections more partisan and established an unlimited hunting season on wolves.