The Economist nails it:

Our prejudice is firmly in favour of a leaner state, but the Republicans need to recognise, as their intellectual forebears did from Adam Smith to Abraham Lincoln, that government has an important role to play in a capitalist economy, providing public goods and a safety net. Teddy Roosevelt broke up over-mighty companies, rather than doling out tax breaks to them. Why on earth are people who champion a small state supporting an expensive war on drugs that has filled the prisons to bursting point without reducing the supply of narcotics?

But the Republicans’ main problem is taxes. Successful deficit-reduction plans require at least some of the gap—perhaps around a quarter—to be closed by new revenue. If the Republicans got rid of loopholes, they could cut all the main tax rates and still raise more money.

But they are stuck on Norquist.