For a guy who called Joe Sestak's campaign viable back in the lonely days of winter, I started second-guessing even as everyone else was warming to the guy. 

That's what they call being a contrarian. Or just plain neurotic. But whatever you call it, I'm not alone. I know more than a few people who began feeling "buyer's remorse" after Sestak beat Arlen Specter in last week's primary. A few of them sound, somewhat belatedly, like Arlen Specter's backers sounded a few weeks ago, worrying about whether Sestak can win in November.

It's to those second-guessers -- the people just like me -- that this post is addressed. 

Let's admit the obvious. If you're worrying that Joe Sestak is going to have a hard time beating the GOP's Pat Toomey this November, Sestak's appearance on Meet the Press yesterday won't assuage your doubt's. Sestak's answers to questions -- especially concerning whether the Obama administration offered him a job to drop out of the race -- sometimes sounded evasive. (Although judging from coverage elsewhere, it doesn't sound like Sestak dreamed up the job offer on his own.) 

Too, at least some evidence suggets that part of Sestak's support was coming from an "anyone-but Arlen" constituency. Note, for example, that Sestak has polled well among voters who thought health-care reform was a bad idea, even though Sestak voted for the reform too.

It's a good bet that Toomey will try exploiting that little paradox. That's why Gregory's questions about Sestak's support of the Obama agenda sounded a bit ominous to me.

Another worry: Does Sestak really have the ground game he'll need for November?

That sounds like a dumb question considering last week's result. And when I put the query to Sestak supporters on Election Night, city councilor Doug Shields told me, "You've just seen the ground game. We didn't have any help from the party establishment." He pointed out that no matter how the endorsements went this spring, groups like labor will certainly back Sestak in the fall. A victory for Toomey, who has long been affiliated with the anti-labor Club for Growth, would be too awful to consider.

Still, there were fewer than 50 people at Sestak's Pittsburgh HQ on Election Night. I've got a feeling that won't be enough: Rank-and-file Democrats turned out to vote against Arlen Specter, but that doesn't mean they'll be as motivated to vote for Joe Sestak.

So let's acknowledge all those concerns, second-guessers. And let's be glad Sestak won anyway. Because no matter what happens in November,his candidacy was a good thing.

First and most obviously, the threat of a Democratic challenger kept Arlen Specter in line for a year of critical votes, most notably on healthcare. God only knows what he would have done without Sestak waiting in the wings. 

Second, the fact that Sestak was in the race may have brought more Dems to the polls last week. And if GOP spinmeisters can be believed, that turnout have spelled defeat for the GOP in a critical special election to replace John Murtha. Granted, that explanation for the GOP's loss may be an attempt by Republican insiders to cover up their own shortcomings. But to me, it's not too big a stretch to say Sestak inspired folks to turn out -- either to vote for Specter or against him -- once they realized Specter had a viable challenger. 

Of course, if Sestak were to lose in November, having Mark Critz in Congress would be little consolation. (And that assumes Critz will retain his seat in the regular election this fall anyway: That race will be a rematch with Republican Tim Burns.) But here's the thing: I truly don't believe Arlen Specter would have beaten Toomey anyway. 

I've sort of been bemused by all the attention given to Sestak's attack ad on Specter, which is widely being touted as the turning point in the race. Didn't we all know that ad was coming? If Sestak hadn't aired something like it, Pat Toomey would have. And then where would we be in November? We've always known Specter didn't have any support among Republicans. What we learned last week is that Dems were never that gung-ho about him either. Would that have changed if Sestak hadn't challenged him? I doubt it. More likely, the lack of Democratic enthusiasm would have manifested itself in November, when we could least afford it. 

So what's the worst-case scenario of this Sestak win? Sestak loses to Pat Toomey, an ultra-conservative in the Rick Santorum mold. That'd be bad, but there's a good chance Specter would have lost anyway. Along the way to November, meanwhile, Sestak's presence in the race ensured a reliable vote in the Senate for healthcare and other Democratic initiatives. And whenthe primary itself rolled around, Sestak may have helped capture a critical swing seat in a special election. That result gave Dems across the country a bit of badly-needed optimism in a difficult year. It's already paid dividends in the form of an especially idiotic Jack Kelly column which contends that somehow, the win was actually a bad thing for Democrats. (Does anyone think Kelly would have made the reverse argument had the GOP come out on top? Anyone?)

So let's be of a resolute good cheer and move forward -- without taking anything for granted, but also without the self-doubt that so often afflicts those of us on the left. Sestak has already been a winning proposition. And this is just getting started.