Hillary Clinton keeps selling, but superdelegates aren’t buying, at least not in enough numbers. There’s a report by the New York Times today that Democratic Party superdelegates wooed by Clinton (and of course by her well-connected husband) haven’t responded, and in fact five more superdelegates in the last two days announced commitments to Barack Obama.

The math — the pursuit of that magical 2,025 delegates figure — isn’t looking good for Clinton. As Obama opens an office 80 miles north of here in Sioux Falls with an eye to the June 3 South Dakota primary, it’s likely the nomination will be wrapped up before that. To date, Obama has 1,650 delegates (1,416 delegates and 234 superdelegates) and Clinton has 1,511 (1,252 and 257 superdelegates). With proportional division of delegates — if a candidate gets 60 percent of the vote, he or she gets 60 percent of the delegates — instead of winner-take-all, it will be hard for Clinton to gain ground. Her polling lead in the April 22 Pennsylvania primary is waning, and if she only eeks out a win or loses, there will be pressure to drop out.

Rick Mullin, a former Woodbury County Democratic Party chairman and an Obama supporter, says proportional division of delegates ensures Clinton can’t win.

“He’s in such a strong position compared to Mrs. Clinton,” Mullin said. “I honor Sen. Clinton and her supporters, but the fact is that I’m virtually certain that Sen. Obama is going to be the nominee and that he’s going to be the next president of the United States.”