Sen. Sherrod Brown, D-Ohio, is fighting for Social Security disability insurance for the millions of Americans who use it. He's saying it's not enough to protect the current model of how the insurance works: Now is the time to expand and grow the program.

"We need to do more than defend the program and play defense," Brown said at the Center for American Progress on Tuesday morning. "We need to play offense. We need to expand the program."

Social Security has recently come under attack by some members of the GOP. Sen. Tom Coburn, R-Okla., argues that a third of the claims are bogus, and that puts financial strain on the program.

Sen. Orrin Hatch, R-Utah, has called for a hearing on Social Security disability insurance, which may take place later this month.

The Social Security Disability Insurance Trust Fund is set to run out of money in 2016.