Sens. Ted Cruz (R-Tex.), left, and Rand Paul (R-Ky.) wait to speak at the "Exempt America from Obamacare" rally on Capitol Hill on Sept. 10, 2013 in Washington, D.C. (Drew Angerer/Getty Images)

The Republican Liberty Caucus, a 25-year old union of the GOP's libertarian-leaning activists, has endorsed Sen. Rand Paul (R-Ky.) for president over Sen. Ted Cruz (R-Tex.). Coming just hours before Paul gets a Senate vote on his legislation to audit the Federal Reserve, his campaign is calling this a victory in the "liberty lane" of the Republican primary.

"Senator Paul is the candidate of choice among our state charters and membership at large,” said RLC National Chairman Matt Nye in a Tuesday morning statement. “Senator Paul has been a consistent favorite with our members since he announced his candidacy."

As Paul's presidential campaign has worked to regain footing in the primary, it's beseeched libertarian-leaning Republicans not to join Cruz's bandwagon. That effort has largely succeed, with some close calls. In October, the Paul campaign worked hurriedly to win a straw poll at the RLC's New Hampshire-based convention, where Cruz made a surprise appearance. When a confusing two-ballot system handed Paul the win, Cruz's campaign declared partial victory anyway, noting that "51 percent" of the combined ballots were marked for Cruz. Paul's campaign, which blamed Cruz for rumors of internal disarray, bragged that Cruz had been "conquered."

In the ensuing weeks, despite well-received debate performances, Paul continued to lag behind Cruz. On Jan. 3, RLC National Director Steve Hoffman told the blog Conservative Fifty that he was personally switching from Paul to Cruz. "At our recent RLC national convention, Paul and Cruz were nearly tied in our straw poll, with Rand being a few points ahead," he explained. "So it’s clear that within the RLC, Cruz and Paul stand out as the two acceptable candidates."

Paul has sharpened his rhetoric about Cruz; in a series of half-festive, half-revealing New Years tweets, he resolved "to give @TedCruz more lead time before I announce my policy positions, so he can replicate them faster." Had the RLC issued no endorsement, after endorsing Paul's father in the 2012 primaries, it would have hinted at serious defections from his base. But two-thirds of RLC members, many of whom entered or re-engaged with politics because of Ron Paul's presidential campaigns, prevented catastrophe.

Cruz's campaign, which has alerted reporters to any defections from Paul's camp, was sanguine about the RLC vote.

"The reason our campaign has been so successful is because conservatives, including many in the Liberty movement, are supporting Ted Cruz," said Cruz spokesman Rick Tyler. "We did not expect the endorsement of the NH RLC but we are proud to have the support of many of its members."

Paul's campaign, meanwhile, was boasting of an unconditional victory.

"As the only liberty-minded candidate," said Paul spokesman Sergio Gor, "Senator Paul is very pleased and grateful to the Republican Liberty Caucus."