There are several decades long narratives in American politics which people (with a perpetual Villager assist) have long internalized. Democrats are pacifist wimps who want to give all your money to undeserving poor people. Republicans love to cut taxes and to cut government spending. Democratic political consultants seem to be forever trying to fight against these narratives, without seeming to understand that it's very difficult to dislodge them. The problem that arises is that if you start beating the deficit drum, then you haven't made voters "trust you" on the deficit, you've made the case to voters that they should elect the Republicans who will be better on this very important issue.
Of course enlightened Eschaton blog readers know that Republicans are full of shit on spending and to a lesser extent taxes, but David Gregory is never going to explain that to the rest of the country. If you make the case that Republican issues are important, you're making the case for...Republicans.
But it's brilliant politics!!!