Last night Joe Scarborough spent several minutes harping on a favorite talking point of the Clintonites. If Barack Obama can’t win primary races in the big states that Democrats need in November, he kept demanding, then how could Barack Obama win those states against John McCain in November?

Let’s rehearse the underlying logic of the argument using leafy vegetables as our proxies. If spinach proves less popular than arugula with around half the voters in a given state, how could spinach possibly be more popular than wilted romaine among the totality of voters in that state?

It’s a non sequitur. The fact that Hillary Clinton has beaten Barack Obama in a number of big states with traditionally strong Democratic machines doesn’t tell us that Obama can’t beat McCain in those states. It doesn’t tell us that Hillary could. In themselves, the big-state Democratic primaries don’t tell us anything at all about a general election.

Clinton’s strong performance in states like Ohio, Pennsylvania, and New Jersey is in significant part a testament to the ties of loyalty that many party functionaries in those states still feel toward the Clintons and the national Democratic party that Clintonites have long controlled. Hardly surprising she gets the better of intra-party organizing battles on the ground there. But again, not really probative when it comes to assessing a Democrat  v. McCain race.

By way of postscript, I’ve encountered one line of analysis that makes a plausible case Obama does have a big-state problem. Several weeks back I read an piece — which I neglected to save; if you’re familiar with it, please post a comment or drop us a note — indicating that Obama seemed to do well in states with very small or very large African-American populations, and less well in places where black people comprised 5-15 percent of the population. Less well, in other words, where there is a black population large enough to keep the racial fears and animosities of whites actively in play, but not large enough to make a decisive electoral difference in Obama’s favor. I don’t know whether it’s so, but in a campaign where it’s been too easy to pretend that America simply woke up color-blind one day, it bears examining.