In South Dakota’s special House election yesterday, Democrat Stephanie Herseth defeated Republican Larry Diedrich, 51 percent to 49 percent. Less than 3,000 votes separated them. They will almost certainly square off again in November, but Herseth will have the advantage of incumbency. Perhaps Diedrich will preveail, especially with Bush on the top of the ticket. Still, it would have been very nice to see him win yesterday and go into the fall with a leg up. The president campaigned to prop up a teetering Arlen Specter in April; couldn’t he have visited South Dakota to help pull Diedrich over the line? This is a contest that shouldn’t have slipped away.