GOP plots Pennsylvania onslaught as Democrats battle to keep ‘really difficult’ Senate seat

For more on CNN’s coverage of the US Senate race in Pennsylvania, watch CNN’s “Inside Politics with Manu Raju” on Sunday at 8 a.m. ET and 11 a.m. ET.

Sen. Bob Casey is bracing for a GOP onslaught.

After a summer where he and his GOP opponent, David McCormick, have engaged in a brutal exchange of attacks in the marquee US Senate race in Pennsylvania, leaving the race in a dead heat, Republicans are preparing to drop more than $100 million across the airwaves in the final two months of the campaign.

The staggering sum, which accounts to roughly $40 million more than Casey and his allies are preparing so far, gives McCormick the biggest edge on the airwaves of any Senate candidate in the campaign’s home stretch. Up until this point, both sides had spent similar levels on air, with Casey holding the advantage.

“I think I’m the underdog,” Casey, a three-term incumbent with a long history in Pennsylvania politics, told CNN after a Philadelphia rally with union workers. “Those corporate super PACs that are coming in here, that have already begun to attack me all summer long, those expenditures are going to go up exponentially.”

While Casey still predicted he would pull off a November victory and contended that he didn’t “care what they spend,” he said: “I don’t have a personal super PAC funded by Wall Street billionaires. … It’s going to be a really difficult race to win.”

Casey’s comments underscore the larger Democratic struggle to keep control of the Senate. They need to hold all their seats – other than West Virginia, which is almost certain to flip to the GOP – in order to simply keep a 50-50 Senate. And that means Democrats can’t afford a slip-up in a purple state like Pennsylvania,