The consensus is that she's a hard-right torture lady, so supporting her isn't gaining any swing voters in Indiana. It sounds like he's one of those people who carefully carve out a voting record to make themselves look "moderate" (which has a tendency to mean "a little more conservative"), instead of actually voting the way he feels.
Nobody's going to go into the voting booth and say: "Gee, I was going to vote for Joe Donnelly but he voted against that torture lady in May so I'll go with the Republican."
If anything it's more likely to have the opposite effect and cost him Dem-leaning voters who will simply not vote in the Senate race.
