President Barack Obama says Mitt Romney and running mate Paul Ryan get a failing grade on explaining how they'd pay for trillions of dollars in tax cuts.
The two Republicans were asked separately on different Sunday morning talk shows what loopholes they'd close to pay for their tax proposal but neither was willing to give specifics.
Obama says that's like saying two plus one equals five. Obama says Romney and Ryan are practicing bad math instead of bold leadership.
Romney says he won't raise taxes on the middle class but will close unspecified loopholes enjoyed mostly by the wealthy to pay for lower tax rates for everyone.
Campaigning along Florida's space coast, Obama also highlighted NASA's recent Mars landing. He praised what he called "a new era of American exploration."