SNOWE RISKING PUNISHMENT…. If Olympia Snowe supports health care reform, her Republican colleagues will be more than just annoyed.

Sen. Olympia Snowe (Maine) is risking a shot at becoming the top Republican on an influential Senate committee by backing Democratic healthcare legislation, according to senators on the panel.

A Senate Democrat on the Commerce, Science and Transportation Committee said Republicans on the panel are threatening to vote against Snowe, who is in line for the senior GOP post that is about to come open.

“Wake up,” the Democrat told a reporter last week when questioned if the Republicans would retaliate against Snowe for crossing party lines.

An unnamed Republican senator on the Commerce Committee said Snowe would be assured of the ranking member post under normal circumstances — the spot will be vacant once Sen. Kay Bailey Hutchison leaves the chamber to run for governor in Texas later this year — but the GOP might balk if she supports health care reform. “A vote for healthcare would be something that would weigh on our minds when it came time to vote.”

Or, put another way, “It’s a nice ranking-member-post opportunity you have here. It’d be a shame if something happened to it.”

It often goes overlooked, but it’s worth remembering that the Senate Republican caucus, unlike Senate Democrats, have mechanisms in place to enforce party unity and discipline. When Democrats break party ranks on key bills, there are no consequences. Those who let GOP leaders down, however, know in advance that enticements like committee positions are very much on the line.

Indeed, there are widespread rumors that Sen. Chuck Grassley (R-Iowa) shifted away from cooperation on reform and towards belligerence immediately after his Republican colleagues made it clear that his future committee assignments were in jeopardy if he worked with Dems to pass a reform bill.

For Democrats, seniority rules. For Republicans, party loyalty can trump all.

Snowe, in other words, may very well be punished for doing the right thing. And she knows it.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.