Kevin Drum gives the spot on answer for the Republicans.
Answer for Republicans: They don’t think the deficit is a problem. If they did, they’d favor tax increases, Pentagon cuts, and Medicare cuts, since even the most dimwitted among them knows that cutting domestic discretionary spending won’t make a dent in the deficit. But they favor none of these things.
Rather, they think federal spending on liberal social programs is a problem, and yammering about the deficit is a good way to force cuts to these programs. And there’s nothing wrong with this. It’s good politics. Why waste a crisis, after all? But anyone reporting on this issue really needs to be honest about what’s going on. Republicans want to cut social spending. The deficit is just a handy cudgel to make this happen.