Romney’s failure to explain the difficult decisions that would have to be made makes it hard to see how he can achieve a balanced budget, said Bob Bixby, executive director of the Concord Coalition.

“It’s saying: I believe in lower taxes and smaller government, except perhaps for defense,” said Bixby, whose Arlington, Virginia-based group advocates for deficit reduction. “That’s really a theme, but he’s yet to show how the numbers add up.”