The group had run ads early on slamming Murphy as a "liberal" and criticizing some of his votes, but has been silent since — and with the primary just two weeks away, it's unlikely they'll get involved.

Former Capitol Hill staffer Evan Feinberg (R) showed some early promise, and secured the backing of his two former bosses, Sens. Tom CoburnTom Coburn'Path of least resistance' problematic for Congress Freedom Caucus saved Paul Ryan's job: GOP has promises to keep Don't be fooled: Carper and Norton don't fight for DC MORE (R-Okla.) and Rand PaulRand PaulThree more GOP senators announce opposition to healthcare bill Rand Paul: Trump 'open to making bill better' Senate GOP delays ObamaCare repeal vote past recess MORE (R-Ky.). Both are popular with fiscal conservatives and Tea Party members. But Feinberg has struggled mightily to raise money — he'd raised less than $50,000 by the end of the year.

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"There have to be a lot of dynamics in place for us to get involved in a race. Feinberg hasn't raised much money," Chocola said. "We don’t mind being one of the larger financial supporters of a candidate but we don't want to be their finance committee. We think he's great on the issues but you have to be viable."

Murphy released a mid-February internal poll showing him with a 74 to 12 percent lead, and should be in a strong position for reelection. But he's not quite out of the woods: the Campaign for Primary Accountability, a deep-pocketed super-PAC targeting incumbents of both parties, is spending more than $200,000 in attempt to defeat him.

—This post was last updated at 6:02 p.m.