Tax cuts are not conservatism. They are not a coherent worldview. They were a part of the conservative philosophy, but not an end in themselves. Stripped out of the larger framework of smaller government, of modesty about the possibilities of change, of respect for tradition and history, and of the sense that central government can be oppressive as easily as it can be liberating, tax cuts amount to nothing more than a material benefit for a few, and a long-term liability for everyone else. Put another way, imagine that the animating ideas of liberalism were reduced to this promise: "We will create a new cabinet-level agency every single year." That's not a vision that can attract deep loyalty, and neither is the promise of a tax cut every year.
What, exactly, does the Republican Party have left? It doesn't have a commitment to Homeland Security, witness Bush's opposition to the DHS, 9/11 commission, and a myriad of other HS reforms. It doesn't have a commitment to small government, look at the Prescription Drug Coverage plan. It doesn't have a commitment to states rights, look at NCLB. It doesn't care about government non-intrusiveness, look at the FMA and the PATRIOT act. The closest thing to a coherent foreign policy it has is a commitment to democratization, which I support (and tragically, many Democrats have reflexively opposed despite it being a natural extension of liberal views), but even this appears to have stalled out beyond Afghanistan and Iraq (look at our anemic protests towards Putin's Russia, and our devil's bargain with Uzbekistan, for example). I would say Republican's like to blow things up, but then why is North Korea still on the map? It appears that LITERALLY the only thing that "unites" the Republican party is tax cuts, and that coalition simply can't hold together much longer.
What would be interesting is seeing what the "new" GOP will be. In discussing it with my friends, the most popular answer is that the Rockefellers will united with the "traditionalists" (IE, McCain and his ilk), with the libertarians still cautiously supporting them (but, like today, being relegated to the margins), and the social conservatives being the odd men out. They justify this on two grounds, first, that the social conservatives are the farthest from mainstream American thought and thus would be logically the first to be jettisoned, and second that since American youth are more tolerant than their parents, the religious right is a shrinking demographic anyway and thus won't be able to wield as much power. I lean more towards the social conservatives taking control, taking about 3/4 of the traditionalists with them. The Rockefellers, Libertarians, and remaining Traditionalists will become independents or possibly Democrats. The reason I think this is true is that, even if their numbers are naturally shrinking, the religious right still is by far their largest constituency and biggest voting bloc. Not only do they keep the deep south and plain states firmly in Republican hands (and let's remember, the south's Huey Long roots mean it doesn't have any emotional attachment to small, limited government per se, same thing for turn of the century prairie populism, neither has deep, longstanding mistrust of government), but they also represent the GOPs best argument towards otherwise democrat leaning constituencies in swing states. Look at Ohio, for example. There, the GOP isn't selling its economic message to prospective voters, it's seeking to lure voters to the polls by virtue of the anti-gay marriage initiative on the ballot. On economics, they lose, on social policies, they win, and that's why the social conservatives will have disproportionate leverage in the party. Simply put, the social conservatives can reasonably argue that they can create a winning electoral strategy without anyone else's help, which may or may not be true but gives them a lot of maneuvering room in the chaos that is to come. The Rockefellers and Libertarians simply aren't prevalent enough in the GOP base to really influence the party (the former concentrated in the solidly Democratic Northeast, the latter rarely seen outside of Dupont Circle in DC). This grip is only strengthened by virtue of the fact that the vast majority of the Republican leadership is in the social conservative wing (DeLay, Kyl, Santorum, Hastert, Bond, etc). If the moderates wish to take control of the GOP, they'd have to mount a coup, if the social conservatives wish to stay in control, they just have to let the moderates die of attrition. Ultimately, demographics work against this new party, and it will drift back towards the center. But in the short term, I expect the GOP to turn hard to the right, especially if it loses this election.