Even as the party is badly outspent in the early going of the 2014 election, some of their top donors have yet to awaken to the threat. In fact, like Steyer, the party’s rich benefactors are putting their single-issue crusades ahead of the party’s greater interests.

Take Michael Bloomberg. The New York City mayor’s group to combat gun violence, Mayors Against Illegal Guns, spent $350,000 last year assailing another endangered Democrat, Sen. Mark Pryor of Arkansas, over his opposition to a gun-control bill. In a small state, that counts as a heavy buy against an incumbent who can barely hold off attacks from Republicans.

It’s left the Democratic strategists plotting the Senate races scratching their heads. While Democrats aren’t facing the deep internal divisions plaguing Republicans, it only takes a few wealthy liberals to create holy hell in the party’s most consequential Senate races.

“I say over and over, ‘Lord protect me from my friends so I can focus on my enemies,’ ” said Ben Chao, a Democratic operative who runs a super Pac supporting Landrieu and Pryor. “This is an apparent case of that.”