Sen. Jim DeMint today endorsed Nebraska Treasurer Don Stenberg’s bid for Senate, throwing his support behind the GOP primary’s underdog to challenge Sen. Ben Nelson (D) next year.

“Don Stenberg is a lifelong conservative with the principles, integrity, and courage needed to stand up to the big spenders in both political parties in Washington,” the South Carolina Republican wrote in a email to his Senate Conservatives Fund members.

Polling shows Nelson is one of the most vulnerable Democrats up for re-election this cycle if he decides to run for a third term. He’ll decide by the end of the year if he will seek re-election.

Nebraska insiders initially viewed Attorney General Jon Brunning (R) as Nelson’s toughest competition, but a few influential national conservative groups recently threw their heft behind Stenberg. Now DeMint has joined the conservative chorus that already included FreedomWorks and Sen. Mike Lee (R-Utah).

“We have thoroughly evaluated each of the candidates in this race and we’ve waited patiently to see which one would emerge as the true conservative standout,” DeMint continued in the e-mail. “It’s now clear that the conservative movement has lined up behind Don Stenberg, and for good reason.”

Stenberg will need all the help he can get to fill his nearly empty campaign coffers. He reported having a mere $18,000 in the bank at the end of September.

At the same time, Nelson had $3.1 million, Brunning had $1.6 million and a third GOP candidate, state Sen. Deb Fischer, had $206,000 in the bank.

DeMint’s announcement marks the third time he’s backed a GOP challenger or candidate in a contested Senate primary this cycle. He publicly voiced his support for Ohio Treasurer Josh Mandel, who now only faces nominal GOP opposition, and Texas Solicitor General Ted Cruz earlier this year.