Vice President Joe Biden described the Ryan pick as giving "definition to the vague commitments that Romney has made." I think he's right.
We know how Romney won the GOP primary game. He was disciplined. He was skilled. He was better than bumbling opponents. He wooed the base with his mantra of tax cuts, tax cuts and more tax cuts.
The general election is a tougher contest. President Barack Obama and Biden are pros at promising something for nothing. They've convinced their base that the federal government can keep growing -- and in a fiscally responsible way -- if only Republicans would let them tax the top 2 percent of income earners just a little bit more.
Romney can't beat the Democratic ticket at that game, but he can beat them by being the adult in the room. In picking the spending-cut-minded Ryan as his running mate, Romney has become more credible.