Rep. Joe Donnelly is Indiana’s Democratic nominee for U.S. Senate. But his problems have just begun. His biggest challenge is not Richard Mourdock but President Obama, House Minority Leader Nancy Pelosi (D-Calif.) and Senate Majority Leader Harry Reid (D-Nev.)

The dayafter Mourdock’s victory, the conservative Club for Growth is out blasting Donnelly for claiming that he never voted for Pelosi as speaker of the House. He voted for her twice.

But that’s only the beginning of Club for Growth’s complaints. Its spokesman has released this statement: “It’s shocking but not surprising that Joe Donnelly’s first act as the Democrat Party’s candidate for Senate is to pretend he never voted for Nancy Pelosi for Speaker. Next thing you know he’ll claim he doesn’t recall his vote for ObamaCare or Obama’s stimulus. Joe Donnelly is an economic liberal who votes in lock-step with Nancy Pelosi and Barack Obama on nearly every issue, and that’s why Hoosiers will elect Richard Mourdock this November.”

In Vermont or California, Donnelly’s record would not be a handicap. But in Indiana it’s hard to argue he is in sync with the electorate.

Moreover, the additional question Donnelly may face, aside from his votes for parts of the Obama agenda, is whether he’ll support Reid as leader in the Senate. It’s Reid and the Democratic majority that won’t pass a budget, or allow a straight up-or-down vote on the Keystone XL Pipeline. Donnelly can swear until the cows come home that he’s going to support domestic energy development or a balanced budget, but so long as Reid is in charge those are empty promises.

This is not only a problem for Donnelly. In fact, it’s a bigger problem for incumbent Democrats. In an interview with Rep. Paul Ryan (R-Wis.) today (I’ll have more on that this afternoon), he put it bluntly: “I don’t know [Sen.] Claire McCaskill — she’s probably a nice lady — or [Sen.] Jon Tester.” But, without having passed a budget in three years he asks: “How do you say to the voters, ‘Send me back to do more of the same’?”

That record of Democratic senators rubber-stamping the Obama agenda and failing to do the basic parts of their job (e.g. passing a budget) will be a weight around the neck of each and every incumbent up for reelection and for those candidates who have carried Obama’s water (e.g. former DNC chief Tim Kaine). As Ryan remarked to me, Senate Democrats “made a calculated decision on that is it better to do nothing and get blamed for that than show the country what you want to do.” That may have been a poor bet.

And that’s really what the Indiana race and the other Senate contests boil down to: Will voters reward Democrats for supporting Obama and, in many cases, neglecting their fundamental obligations as lawmakers?