"My opponent, Tom Smith, thinks we should take away the guaranteed benefit of Medicare and change it, either by giving someone a voucher, or changing it more radically," Casey said, according to the Philadelphia Inquirer.

Smith said he'd leave the program unchanged for current recipients, then called the Democrats' Affordable Health Care Act "one of the biggest power grabs in this country's history."

Casey also attacked Smith for wanting to eliminate the Department of Education.

The first-term senator has had a lead in all polls of the race, but Smith, a wealthy coal executive, has made it more competitive than most expected by spending millions of his own money on the race. Majority PAC, a Democratic super-PAC, recently went on the air to attack Smith, a sign they saw a tightening race there.