Two important Senate primaries tomorrow remind us that the Tea Party wing cost the Republican Party dearly in 2010, and will likely cost it a bit more in 2012 — while at the same time making sure that Republicans who are elected are solidly conservative and display no interest in making deals, even to get their policy priorities enacted.

In Connecticut, a fairly solid Democratic state, Republicans are poised to reject moderate former member of the House Chris Shays and stick with professional wrestling entrepreneur Linda McMahon, who lost her 2010 bid for the Senate. Democrat Chris Murphy would be favored either way, but Shays might have given him a solid challenge; no one really expects McMahon to do so.

Wisconsin is different: it’s a swing state, and the Democratic candidate, Tammy Baldwin, is a member of the House who might be a bit too liberal for the state. Former Gov. Tommy Thompson might be a slim favorite, but he has to survive a primary first against three candidates: businessman Eric Hovde, arch-conservative former member of the House Mark Neumann, and Assembly Speaker Jeff Fitzgerald. The polling is inconclusive — Fitzgerald appears to be the longshot, but anyone could really win this one.

We all know the story here: Conservatives have made a deliberate choice to push for the most conservative nominee in state after state, regardless of the consequences for November. That’s almost certainly a sensible choice in Texas and Utah; it’s a lot more risky, however, in places such as Wisconsin (although it worked there in 2010), and it’s even more damaging in states such as Connecticut. And an ideologue-only nomination policy may also scare a lot of potentially strong candidates from entering in the first place; that could be why Florida Republicans will be nominating someone who is generally viewed as a weak challenger tomorrow to potentially vulnerable Sen. Bill Nelson.

Mostly, I want to emphasize how important these contests are. Each senator simply matters a lot; small groups of senators matter a lot; for the partisan balance of the Senate, each extra vote matters a lot. That’s far less true in the House, although even there individual members can make a difference, especially if they’re in the majority, and it’s worth paying attention to House races in these two states and also in Florida and Minnesota tomorrow. But it’s not crazy to think that, for example, the fate of a future Supreme Court nomination could ride on what happens in Wisconsin tomorrow.