Democrats have agreed to tie budget cuts to the debt ceiling bill. Many Democrats are open to a truly large budget deal. A normal Republican party would seize the opportunity as the mother of all no-brainers.
But the Republicans have been infected by a faction that doesn't accept the logic of compromise, or the legitimacy of scholars and authorities. This faction has no sense of moral decency and talks blandly about default. This faction has no economic theory worthy of the name. For them, tax levels are everything.
If the debt ceiling talks fail, independent voters will see that Democrats were willing to compromise but Republicans were not. They will conclude that Republican fanaticism caused this default and will conclude that Republicans are not fit to govern.
And they will be right.