Politics
Taking inspiration from commenter Art Deco in this thread, I think it is helpful draw distinctions between Republican candidates who are more liberal than most Republicans and liberals candidates who happen to be Republicans. The second category is, at the congressional level, pretty small at the moment. Lincoln Chafee comes to mind as the most recent example. I'm generally in favor of running primary challenges against such liberal Republicans even if it throws the election to a liberal Democrat. The main effect of such principled liberal Republicans is to give bipartisan cover to liberal initiatives.
The first group (to include Specter, Crist, the Maine Senators) is more complicated. They usually don't have liberal (or conservative) principles. They are running as Republicans in marginal or liberal-leaning constituencies (or maybe even right-leaning constituencies) for complicated and self-interested reasons. Since they are all about themselves, they tend to take losing very badly. They have to maneuver against powerful crosscurrents. Their branding as "moderate" or "independent" Republicans (which consists of voting with the Democrats when they perceive public opinion in favor of a given liberal position) means they will be to the left of the Republican Party. Their need to win primaries among right-skewing Republican primary electorates means they will vote well to the right of liberal (and most "moderate") Democrats. It isn't for nothing that all the moderate Senate Democrats voted for Obamacare and all the moderate Senate Republicans against. I would obviously prefer a conservative to a moderate (or just plain hack) Republican whenever possible. I'm glad we will (hopefully!) have Senators Rubio and Toomey rather than Senators Specter and Crist. But it isn't clear that a trading a moderate Republican for a liberal Democrat is an upgrade.
That doesn't mean we are stuck with the moderate Republicans we have. I think it is possible to get a Republican substantially to the right of Snowe and Collins elected to the Senate from Maine. I don't just mean knocking Snowe or Collins off in the primary, I'm talking winning the general too. It would take the right candidate, a populist message, a prudent, measured, and relevant issue agenda, alot of money and a favorable environment, But that doesn't mean that nominating a badly flawed conservative no hoper (or very little hoper) and giving the Senate Democrats one more consistently liberal vote makes for a better Senate.
The Conservatives/Republicans who slammed Castle and backed O'Donnell are idiots and have harmed the Conservative movement. I'm as red-blooded a conservative as they come, but I understand the political process. If the Republicans gained a 51-seat majority they would control the Senatorial committees. The majority party gets to name the committee chairs and sets the agenda for the US Senate by effectively destroying legislation at the committee level before it can even make it to the Senate floor and bringing to vote legislation they've written. The gavel of the Senate Judiciary Committee would be in the venerable Jeff Session's capable hands when President Obama gets to nominate his third Supreme Court Justice.
The point has already been made: the Tea Party is going strong and the Democrats will be thrashed at the polls, so the DELAWARE SENATE RACE was not the place to stick it to the RINOs.
By the way, O'Donnell is a horrible candidate. I guess those who supported her will have to stop calling Obama inexperienced . . .
The worst part will be hearing Hannity and Rush and Palin bitch about Obama's next SCOTUS appointment, or the GOP's inability to repeal or defund any current legislation (ie Obamacare), or the coming DADT circus, etc etc etc. Their feel-good endorsement helped the Democrats keep the majority.
The problem in both of these posts is that you fail to distinguish between scarcely-adulterated careerists (Specter) and politicians whose complex of views places them at points of the spectrum inconvenient for party whips (John Anderson ca. 1974).
AD the second group you mention certainly exists in social life, and probably in Congress (too many in the House of Reps for a lazy bum like me to keep track of), but I think my description works pretty well for those Senators who crowd the 50 score of ACU ratings (or whatever) and aspiring Specters like Charlie Crist Or to put it this way, if Obamacare had been polling ten points better, I don't think Ben Nelson waits on the Cornhusker Kickback to support Obamcare and at least one of the Maine Senators votes for Obamacare - in return for some money for Maine and/or some not-so-big change so she can claim the mantle of moderate savior. I'm a little less sure if I put Mike Castle in this category but his behavior on repealing Obamcare (first cagey, then supporting repeal after feeling heat from conservatives) breeds suspicion. And while one can explain his refusal to endorse O'Donnell based on her personal issues, it does fit into a pattern of sore loserism from "moderate" Republicans who get beaten by more conservative outsiders.
This is not to say that there aren't consistently liberal or conservative voting members of Congress who vote the way they do not out of conviction but because thats what they think will get them reelected.