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 GrahamLindsey Olin GrahamGraham: Trump’s new AG has ‘concerns’ about criminal justice bill Overnight Defense — Presented by Raytheon — Border deployment 'peaked' at 5,800 troops | Trump sanctions 17 Saudis over Khashoggi killing | Senators offer bill to press Trump on Saudis | Paul effort to block Bahrain arms sale fails Senators introduce Trump-backed criminal justice bill MORE 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."

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Cash said "the origins and foundation of American greatness lies in Christianity, Capitalism, and the Constitution" and promised he was "unapologetically committed to faith and family as the essential elements of enduring freedom."

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 PaulRandal (Rand) Howard PaulHillicon Valley: Facebook reeling after NYT report | Dems want DOJ probe | HQ2 brings new scrutiny on Amazon | Judge upholds Russian troll farm indictments | Cyber moonshot panel unveils recommendations Overnight Defense — Presented by Raytheon — Border deployment 'peaked' at 5,800 troops | Trump sanctions 17 Saudis over Khashoggi killing | Senators offer bill to press Trump on Saudis | Paul effort to block Bahrain arms sale fails On The Money: Senior GOP senator warns Trump against shutdown | Treasury sanctions 17 Saudis over Khashoggi killing | HQ2 deal brings new scrutiny on Amazon | Senate confirms Bowman to Fed board MORE (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.