In North Carolina (50 percent Romney), Democrat Kay Hagan faces a different battleground. The Obama campaign vastly increased turnout in 2008 and won the state then with high black turnout and support from high-education whites.
But that coalition failed to prevail in 2012, when Romney narrowly carried the state and Republicans captured the governorship and won large majorities in the state legislature.
Incumbent Hagan won the seat in 2008 largely because of slipups by Republican Elizabeth Dole. She has come out for same-sex marriage and isn't denouncing Obamacare. Evidently she's hoping to reassemble the 2008 Obama majority.
Another Democratic surprise winner in 2008 was Mark Begich of Alaska (55 percent Romney). He won by 1 percent after incumbent Ted Stevens was convicted on federal charges in October. That conviction was reversed in 2009, but Begich was positioned to cast what can legitimately be called the deciding vote for Obamacare that year.
If Democrats lose all seven of these seats in Romney states, and if Republicans avoid nominating candidates who manage to lose seats that currently seem unloseable, Republicans will have at least a 52-48 Senate majority.
And they have at least an outside chance of winning seats in 2012 target states Colorado, Iowa and New Hampshire, plus Michigan.
Well, you might ask, isn't it unusual for parties to sweep all the close races? Actually, sometimes they do. Republicans did in 1980 and Democrats did in 1986 -- and those were the same seats.
Republicans won the bulk of close races in 2002, and Democrats won the bulk of close races in 2008 -- the same seats again and the ones up next year.
A sweep is by no means certain this time. But if the Obamacare rollout is a "train wreck," as Baucus feared, the odds get better.