Jeanne Shaheen, the senior senator from New Hampshire, won her seat by defeating a Republican incumbent in 2008. She was thought to have a safe seat this year, and most polls and observers still give her an edge, if a tenuous one, over likely GOP challenger Scott Brown.

But she has a problem. Like every other Democrat who was in the Senate in 2009, she cast the deciding vote that caused the so-called Patient Protection and Affordable Care Act to become law. The Granite State is nobody's idea of an ObamaCare success story....