When Senator Olympia Snowe, a moderate Republican, announced that she would not run for reelection, she demonstrated another of the difficult challenges that movement activists face when they engage electoral politics. Senator Snowe would cut deals with the Democratic majority, and showed unpartisan flexibility in dealing with process, schedules, and budgets. At the same time, she voted with the Republican Party almost all the time, and certainly on matters of organizing the Senate.

Apparently her vision of pragmatic conservative politics was compatible with Maine voters; experts, like 538’s Nate Silver, saw her reelection as extremely likely. She had raised plenty of money already, and was hugely popular in the state. (Silver notes, however, that the seat is now extremely likely to go to a Democrat, jeopardizing the Republican effort to take control of the Senate.)

For social movements, putative allies judged insufficiently resolute are attractive targets. Conservatives call their more pragmatic members “RINOs,” that is, Republicans in Name Only, and have targeted them in primary campaigns.

Attacks on the least doctrinaire Republicans, like those who can win in swing districts, was one of the critical stories of the 2010 elections. Sometimes, as in Utah (Mike Lee) and Kentucky (Rand Paul), conservatives replaced the choice of party regulars with more conservative alternatives and won. In other cases, however, including Nevada, Delaware, and Colorado, they succeeded in nominating very conservative candidates who lost winnable races against Democrats.

Pragmatic politicians want numbers, and can work out details about loyalty later. They understand that majorities organize the legislature and make policy, while resolute minorities can make statements and try to stall their opponents.

But primary challenges can have additional effects, and not only on those directly challenged. Fearing a primary challenge, moderates are more likely to protect their flank, eschewing compromise and votes that might later need to be explained to a fundamentalist core that turns out to vote in primaries.

Senator Snowe was facing a primary challenge from a Tea Partier (Scott D’Amboise), like her colleagues Richard Lugar (Indiana) and Orrin Hatch (Utah). Unlike Senator Snowe, Senators Lugar and Hatch would never have been called anything but conservative until this odd moment in American life. They did, however, try to govern. But the primary challenges worked: all three tacked to the right legislatively, paying attention to winning the support of their party first. Senator Hatch even warned that if the Republicans gained the majority without him, Olympia Snowe would be chair of the Senate Finance Committee.

The primary challenges play out differently, depending upon context. While Maine now seems primed to elect a Democrat to the Senate, Utah is virtually certain to elect a Republican senator, even if their candidate isn’t Orrin Hatch. And Indiana is somewhere in between.

Few professional politicians would prefer to be part of a disciplined and unified minority than to participate in a broader coalition that governs. Republican Senator Jim DeMint (South Carolina) is one of them. Politico quotes Senator DeMint:

I don’t want to be in the majority if we don’t have bold ideas and that we’re going to reform government…I think the problem we have as a party is when we are so afraid of losing elections that we’re afraid to do the right thing. That’s what hurts us as Republicans. I think it’s the principles that people relate to.

The challenge we have is not that there’s not room in the party for different people, but there has got to be a party that recognizes that somehow we need to transition toward a smaller, less expensive government…And if there are people in the Republican Party who don’t think we have to do that, there’s probably not room for them.

If Republicans lose this election, Senator DeMint’s position on the longstanding purity versus pragmatism debate will become less and less popular. Tea Party enthusiasm will have cost the Republican Party a seat in the Senate, and compromised its prospects for winning the Senate. In the halls of Congress, Republican legislators are muttering about the need for activists to grow up and get realistic.

Voters, of course, face the same choices that movements do. Holding your nose and voting for the “lesser evil” is another way of saying that you’re making pragmatic choices. (Occupiers looking at President Obama in the Fall will face exactly that purity versus pragmatism choice.) It’s not always pretty or appealing, but this is also what democracy looks like.