I talked with two Republicans recently in two different cities. Both times, when I started discussing how awful the economy has done under Dubya, they said that a President doesn't really have that much of an effect on an economy and that it takes 6-8 years for a President's policies to take effect. Therefore, most of Clinton's boom was because of the effects of Reagan's/the elder Bush's policies and Dubya's economic woes are because of Clinton's mismanagement of the economy. One of them said she heard an economist on NPR who identified himself as a Democrat give this theory and also said that the Depression was not all the fault of Herbert Hoover.
Personally, I think there is a little truth to this, but not much. It may take a while for the full implications of a President's policies to be felt, but most of the effect is felt within 2 or 3 years. For example, when Dubya cut taxes, he was very aggressive about implementing it with the tax cut checks and the mid-year change in the withholding schedules. Most of the effect of getting more money to consumers was occurred within his first year. Now, the later effect of states facing big deficits because they tied their state income tax calculations to the federal income tax calculations came later, but most of the states have already dealt with that. IMHO, the last year has shown the true effectiveness of Dubya's policies and they are much less beneficial for the economy than Clinton's policies (or almost any other President).
Some policies do take a long time to take effect. For example, the full effect of Reagan's Savings and Loan reforms weren't felt until the Savings and Loan bail out was completed under the elder Bush. However, once you say that all policies only have a long-term effect, that any discussion of economic policy becomes an exercise in handwaving. The two Republicans didn't have any evidence to offer to support their theory, but it was a great way to avoid admitting that the Republicans' economic ideas are bunk.
How could I have simply countered this theory?