The top Senate GOP super PAC is going all in on Pennsylvania.

The Senate Leadership Fund, a group with close ties to Mitch McConnell, is laying down a massive $24 million ad buy to help Republican Dave McCormick in his bid to unseat incumbent Bob Casey. It will run for a month beginning Sept. 3 and include broadcast and cable TV, radio and digital components.

The investment is a sign of confidence in Pennsylvania, the first state where the super PAC has reserved air time outside of the more conservative states of Montana and Ohio. So far, the group is following the plans telegraphed by McConnell in the spring, when he said Republicans would play in Pennsylvania, Montana, Ohio and Maryland.

SLF and its allied group American Crossroads have placed $82.5 million in Ohio ad buys for September through late October. In Montana, those two groups have reserved a combined $47.9 million.

The National Republican Senatorial Committee revealed its first round of fall ad buys last week. Its independent expenditure arm is booking airtime in Ohio, Nevada, Michigan and Arizona, while the committee itself is planning joint ad buys with candidates in other states.

McCormick already has his own dedicated group, the Keystone Renewal PAC, which has booked more than $30 million in ads to boost him throughout the summer and fall, according to the media tracking firm AdImpact.