"As a South Carolina state senator, Lee Bright has earned the reputation for being the most conservative leader in the legislature," the website says. "His impeccable voting record reveals a strong belief in Second Amendment freedoms, pro-life values, the advancement of civil liberties and fiscal responsibility. It's time to take this proven track record to the U.S. Senate so South Carolina can lead the charge against the Washington establishment."

Bright joins businesswoman Nancy Mace (R), the first female graduate of The Citadel, and former congressional candidate Richard Cash (R) as challengers running against Graham from the right.

Graham has angered some conservative groups for his willingness to work across the aisle on fiscal issues and immigration. Libertarian activists have also criticized Graham for his hawkish foreign policy views. Bright told The Hill earlier this year that he was in talks with the deep-pocketed Club for Growth about possible help in defeating the well-funded senator, whom polls show is in a fairly strong position.

How serious a threat Graham faces will be determined by whether one of the candidates can unite Tea Party activists, libertarian voters and those unhappy with Graham's immigration positions.