My reading of contemporary Republican thinking is that there is no chance of any attempt to arrest adverse long-term fiscal trends should they return to power. Moreover, since the Republicans have no interest in doing anything sensible, the Democrats will gain nothing from trying to do much either. That is the lesson Democrats have to draw from the Clinton era’s successful frugality, which merely gave George W. Bush the opportunity to make massive (irresponsible and unsustainable) tax cuts. In practice, then, nothing will be done.
Supply-side economics transformed Republicans from a minority party into a majority party. It allowed them to promise lower taxes, lower deficits and, in effect, unchanged spending. Why should people not like this combination? Who does not like a free lunch?
This is extraordinarily dangerous. The danger does not arise from the fiscal deficits of today, but the attitudes to fiscal policy, over the long run, of one of the two main parties. Those radical conservatives (a small minority, I hope) who want to destroy the credit of the US federal government may succeed. If so, that would be the end of the US era of global dominance. The destruction of fiscal credibility could be the outcome of the policies of the party that considers itself the most patriotic.
I’m not sure that I agree that supply-side economics was the dominant factor in transforming Republicans from a minority party into a majority party; I don’t think the Republicans have been a majority party for many of the past 30 years and, to the extent that they have been, regional realignment based on opposition to civil rights has been the most important factor, IMHO.
That said, the supply side myth is, truly, economic crack cocaine that has the potential to bring about something as cataclysmic as a US government default — something many conservatives say they would welcome. The only thing that is likely to stop it is a demographic trend that may marginalize the Republican party.