Both men told The Hill in December that they might endorse Feinberg.
Paul described Feinberg as "a tireless advocate for limited government and individual liberty."
Feinberg has generated a lot of attention from Washington conservatives: FreedomWorks has endorsed him already, and the deep-pocketed Club for Growth has been hitting Murphy as a "liberal" in television ads. But he has so far struggled to raise much money, with only $40,000 in the bank at the end of the year.
The two are squaring off in a Republican-leaning congressional district outside Pittsburgh. Democrats are hopeful that they can make the race a competitive one if the more-conservative Feinberg wins the primary.