Businessman Tim Burns (R-Pa.) announced Wednesday he’ll challenge Sen. Bob Casey (D) next year, joining an already large Republican field.

“Our current leadership has made their choice — more spending, more debt, and they have conceded America’s exceptional place in the world,” Burns said in a statement.

Republicans believe Casey is vulnerable, and a recent Quinnipiac survey showed the first-term Senator with a lackluster 46 percent approval rating.

But none of Casey’s opponents are well-known statewide, including Burns, which makes it a tough race for Republicans. The same poll showed Casey leading an unnamed GOP challenger, 50 percent to 31 percent, among 1,370 registered Keystone State voters questioned Sept. 21-26.

Burns ran twice unsuccessfully for the late Rep. John Murtha’s (D) southwestern Pennsylvania House seat last year. One of Murtha’s top aides, Mark Critz, defeated Burns in a May 2010 special election and in the November election for a full term. The latter contest was extremely close, and Burns lost by fewer than 3,000 votes.

In addition to Burns, businessman Steve Welch, tea party activist Laureen Cummings, attorney Marc Scaringi, and former coal-mining company owner Tom Smith are running for the GOP nod.