Jay Cost is known in the conservative blogosphere and beyond as a statistical and polling wizard. But he’s also a source of common sense. He clarifies the presidential choice before Republicans, making two salient points:

First, this year is not going to be like 1980: Even though the economy is extremely weak, Obama will have the near-unanimous support of the Democratic party, while Carter suffered substantial defections. This suggests that the base vote for President Obama in November is probably somewhere around 45 to 47 percent, which has been the floor performance for the Democratic party over the last quarter-century.

Second, the independent vote will be determinative. Roughly 7 to 10 percent of the public in the dead center of the electorate is not anchored by strong partisan or ideological sentiment; these are the only true swing voters left in the country. According to the latest reading from Gallup, these “pure independents” give President Obama an approval rating of just 35 percent; their lack of strong roots in either party tradition, however, suggests that neither side should take their votes for granted.

Thus, the ideal Republican nominee is a candidate who can articulate the party’s conservative worldview in a way that attracts the sliver of the electorate that is actually up for grabs. By the same token, a nominee who alienates the center is a danger in an electoral battle that will unify the Democrats around Obama. With a base vote of about 46 percent, Obama needs only to split the pure independents to be favored for a second term. As the battle for the Republican nomination continues, one question primary voters will have to ask themselves is: Which candidate can best articulate conservative principles and policies to attract, not repel, these independents?

As for the economy, it may well be that the Democrats and their spinners overestimate the economic comeback. Unemployment is more than 8 percent, President Obama has done nothing about the looming debt and economic growth is anemic — is Obama really going to be able to gin up the base and keep all the Democrats in the tent?

That said, Cost is almost certainly correct that Obama will hold on to the vast majority of Democrats, although turnout may be lower than in 2008. (After an election-year pullout of troops from Afghanistan, a no-entitlement reform budget and endless class warfare, it would be shocking if he didn’t get over 90 percent of Democrats.)

So what about those independents in the center? Well, the right-wing base’s angst over Mitt Romney — he’s a pragmatist, doesn’t speak like a conservative, won’t eliminate capital gains for the rich, isn’t for privatizing Social Security and wants to keep federal Medicare as an option under a premium support plan — strongly suggests that he isn’t likely to repel many voters “in the dead center of the electorate . . . not anchored by strong partisan or ideological sentiment.” Certainly his tone and demeanor are not going to come across as strident.

Now you may be confused if you followed the 2008 race. Then, most talk-show hosts and many bloggers who now vilify Romney praised him as the conservative in the race and never even mentioned Romneycare. Actually, Rick Santorum did, too. Romney hasn’t changed since then, but the conservative wailing this time around (who but those inside the Beltway remembers all the way back to 2008, anyway?) that he’s a “moderate” doesn’t appear concerned with consistency.

But getting back to the race this year, Rick Santorum claims to be the “real conservative.” Even if his record is pockmarked with lapses (on free trade, Medicare Part D, right-to-work, etc.), his rhetoric and tone can’t be considered as lacking “strong partisan or ideological sentiment.” He is the flip-side of Ronald Reagan, whose ideology was consistently conservative but whose outward demeanor was charming and soothing. (When the bogeyman the Democrats concocted didn’t show up in the 1980 debates, Reagan was home free.) Santorum is not exactly a happy warrior and he doesn’t have the knack for putting people at ease. (Fire up the partisans he can do, but sweet talk the skeptics is not a skill he’s shown.)

He is, however, the one who will have to explain a host of statements and positions about working women, gays and contraception to those not-very-political voters in the middle. (Those would be the ones that hate super-partisanship.) Conservatives who think voters in the middle will be fine with very extreme positions on these issues articulated in dogmatic fashion haven’t been paying attention to popular culture and behavior, which has become increasingly tolerant.

Now normally, pols run to the extreme in the primary and then back to the center in the general election. But Santorum has never been one to trim his sails for expediency or pass up a fight. In other words, he’s too honest to fake being a reasonable moderate.

Maybe Cost is wrong. Maybe the old “turn out the base”strategy could prove to be a winning one for Santorum. But if Republicans concede the race is about that 7-10 percent in the middle, you have to wonder if Santorum could get more than a smidgen of that dead-center segment of voters “not anchored by strong partisan or ideological sentiment.” Those people sound just like the portrait of Romney conservatives have been painting.