More important, among those 23 Democrats who face voters in 2012 are a handful of incumbents from the kind of moderate to conservative states where Democrats took a beating last week: Ben Nelson of Nebraska, Jon Tester of Montana, Jim Webb of Virginia and Claire McCaskill of Missouri. Joe Manchin, who just won a Senate race in West Virginia by separating himself from President Barack Obama and his party’s congressional leaders, also faces voters again in two years because he was elected only to fill out an unexpired term.

Sen. Mitch McConnell, the Republican leader, looks at this field and thinks he may see some votes for his side. He points in particular to his desire to roll back parts of this year’s big health bill…

So maybe there also are Democrats prepared to drift to the Republican side on issues beyond health—say, on spending cuts, tax levels and a new energy program built around such items as electric cars and clean-coal technology. On selected issues, that means Mr. McConnell actually might find it at least as easy as the Democrats’ Mr. Reid to assemble a working majority.

Of course, there are distinct limits to how much that means in the ever-messy Senate. In a body where any 41 members can mount and sustain a filibuster to stop action, having a bare majority, real or functional, has limited impact.