Cash, a social conservative activist who narrowly lost a House primary runoff election to now-Rep. Jeff Duncan (R-S.C.) in 2010, said Graham has lost touch with South Carolina values.
"I am running to replace Senator Lindsey Graham because I believe that after 20 years in Washington he is out of touch with South Carolina values and voters. Although Senator Graham might be hard-working and sincere, I cannot distinguish his core principles and can no longer trust his judgment," he said on his website.
"It is time for a new voice in Washington. We need a voice that represents Christian, conservative, and Republican principles instead of the latest bi-partisan 'deal' that simply makes matters worse."
Polling shows Graham is in a fairly strong position for reelection. But some on the right are unhappy about his bipartisan work on a number of issues, such as immigration reform. Libertarians in the party don't like Graham's foreign policy views and are still furious about his attacks on Sen. Rand Paul (R) following the Kentucky senator's talking filibuster of President Obama's CIA director nominee, John Brennan.
Other Republicans are mulling a challenge to Graham as well, including state Sen. Lee Bright (R) and Paul backer Nancy Mace.