A Gallup poll shows that Americans oppose both tax hikes and benefit cuts as a way to shore up Social Security and Medicare, but tax increases are more popular than spending cuts:

The odd thing is that the deficit commission seems to be coalescing around a solution that would consist entirely, or almost entirely, of benefit cuts. The dynamic here is that Republicans do not care about the deficit. At all. They are happy to denounce the deficit during democratic presidential administrations, and they will gladly use concerns about the deficit to oppose any new social spending, including social spending that's part of a deficit-reduction proposal. But they don't care about the deficit per se. There is nothing in the post-1990 history of the GOP that displays any concern about deficits whatsoever.

In any relationship, the party that cares the least about winning an according has the upper hand. That's what you're seeing out of the deficit commission. Republicans don't care about reducing the deficit, so they'll only support a plan that consists entirely (or almost entirely) of spending cuts. If it fails, fine. Most Democrats do want to reduce the deficit, so at least a significant core of them are willing to sign off on a solution that's far from their ideal mix.

And so even though public opinion would seem to dictate a solution that leans more heavily on tax hikes, the deficit commission is going in the opposite direction.