(1) Growth in the size of the government, as measured by employment and spending.
(2) Lack of fiscal discipline, as measured by budget deficits.
(3) Lack of commitment to price stability, as measured by pressure on the Fed for easier monetary policy when politically advantageous.
(4) Departures from free trade.
(5) Use of government powers to protect and subsidize favored special interests (such as the oil and gas sector, among many others).
Hard to argue with this list of economics departures from conservative principles and hard to argue that George W. Bush has not violated the first two and the last two. Ronald Reagan does not fare well based on these criteria either and #3 seems to be directed towards Nixon. As Jeff notes:
I would contend that, not just George W. Bush, but also Richard Nixon, Ronald Reagan and (to a lesser extent) George H.W. Bush, all - in sharp distinction from their conservative rhetoric - in practice have been interventionist. They have all wandered, far from the principles of good neoclassical economics, and far from from the principles of small government and laissez faire. How far? Farther than did, for example, Jimmy Carter and Bill Clinton … Documentation that Republican presidents have since 1971 indulged in these five departures from “conservatism” to a greater extent than Democratic presidents can be found in some writings of mine, listed below. The name I would give to this set of economic policies, as well as to the parallel abuses of executive power in the areas of foreign policy and domestic policy, is neither “liberal” nor “conservative” but, rather, “illiberal.”
Jeff also offers a link to a 2003 paper that he wrote on this topic.