Jennifer Rubin looks at Arlen Specter’s decision to switch parties, and sees an opportunity for Republicans, as well as a challenge:

…the challenge for Republicans: to find a message and candidates who sound broadly conservative themes but appeal to an audience beyond the base.
Frankly, that shouldn’t be hard these days. With market capitalism under assault and polling showing voters quite concerned about spending, debt, and bailouts, you’d think Republicans could find a message which resonates with a wide audience. Although perhaps rank amateurs, the tea party protestors have found the message around which conservatives can unify and which might also bring in independents. Personal responsibility, ending corporate welfare and bailouts, reasonable budgets, and the rule of law might form the basis of a winning message.

But in an all-too-familar pattern, the Scylla of a broad-based theme runs right into the Charybdis of fussy litmus tests:

One man’s diversity is another’s heresy. And until Republicans and their loudest voices in the blogosphere drop the “check-the-box” litmus tests they will likely find themselves in the permanent minority.

Here the Democrats hold a distinct advantage. They can claim to have a broad mainstream theme (and they have the media to buttress this claim and make it look downright credible), and their diversity/coalition mentality means that all boxes are automatically checked on all liberal litmus tests, without regard to consistency, or verification. Inconsistency and even dishonesty are ignored, which means that Barack Obama is free to oppose gay marriage for religious reasons — something no Republican could do without being forever consigned to the darkest realms of religious right Christianist theocracy. Democratic litmus tests mean nothing, while Republicans are subject to the strictest possible scrutiny.
Specter has of course been called a RINO for many, many years. As the Club for Growth puts it, such deviations epitomizes what the voters hate:

Arlen Specter is the epitome of everything voters have come to hate about the Republican Party–the desperate grasping for power and the complete rejection of the principles the Party claims to stand for.

The problem with that argument is that if the voters so hate Specter for that, then why has he won so overwhelmingly in every recent election? And why has Santorum lost?
David Frum has a different view:

For a long time, the loudest and most powerful voices in the conservative world have told us that people like Specter aren’t real Republicans – that they don’t belong in the party. Now he’s gone, and with him the last Republican leverage within any of the elected branches of government.
For years, many in the conservative world have wished for an ideologically purer GOP. Their wish has been granted. Happy?

I have no idea whether I’m happy about this. I’ve long since given up on a GOP which is ideologically pure according to my libertarian principles. I held my nose and voted for Specter because I thought he was better than the Democrats. Now that he is a Democrat, I still think he’s better than most Democrats.
But is he better than Toomey? I didn’t think so when I voted in the Republican Primary, because I thought winning against the Democrats was more important, and I didn’t think Toomey could ever win. Not that either man would ever be a match with my litmus test, but I’m not the voting majority. What I think has happened is that Pennsylvania voters have moved to the left at the same time the Republican Party has moved to the right. If such a trend continues, it begs the question of whether the Republicans can win.
But maybe I should stop fretting like a RINO about whether the Republicans can win.
Isn’t it better to lose an election than lose a litmus test?