Mark Sanford's special election campaign announced Thursday that it has earned the endorsement of Sanford's former House colleague, Ron Paul.

"Mark Sanford has always been a strong ally of the Liberty Movement. Help him get to Congress. Donate today!" Paul wrote in a fundraising appeal for Sanford.

It's Paul's second key endorsement of the day. Earlier, he backed libertarian-leaning Rep. Paul Broun in the Georgia GOP Senate primary.

Sanford is running in a conservative-leaning Charleston-based district. While Paul's appeal is somewhat limited within the GOP, his supporters are devoted and generous with their money -- both of which could help Sanford down the stretch in a low-turnout special election.