I am horrified to think of a Republican President's response to the 2008 recession and housing collapse, it could ultimately end up with a Democrat winning in 2012 considering the Tea-Party movement etc etc.
We must also ask will the prosperity and economic boom in the 1990's continue on into the 21'st century because the U.S. did have a surplus from 1999 - 2002 when George W. Bush launched the United States into a every expanding debt hole.
Actually, you'd be looking at a radically different history of the 2000s. As a Texan who remembers Bush's governorship, and who remembers a lot of the conservative reluctance about Bush's presidential run, with no 9/11, you'd see a radically different Republican Party than the Tea Party or the Populist Trump wing. "Compassionate Conservatism" I truly think was not a buzzword for W, and I think it was both pragmatism and ideals that would have led to a major realignment in American politics. Bush governed as a moderate in Texas, and there's a very good reason the Moderate-Liberal Texas Lieutenant Governor and chief power broker, Bob Bullock, endorsed and encouraged W's presidential run before his death.
The end result would have likely forced the libertarians out of the Republican party altogether, as it would become something akin to a more economically conservative version of European Christian Democracy. The voucher programs (very popular among minority communities at the turn of the century), prescription drug coverage, No Child Left Behind, immigration reform, and even the Social Security partial privitazation (which got very unfairly demonized, since it would have gone into the index fund based Federal Thrift Savings Program, not individual stocks). 9/11 threw
everything off course, and it allowed the Democrats to become the Bigger Tent. Without a war to shift his focus, Bush would have been able to build a broad Economically Moderate/Socially Conservative Right-Center coalition, leaving the left and the libertarian right out in the cold.
The Housing crisis is a big one, and a bubble had been building for years. I remember reading articles basically back in 2004-05 to the effect that a bubble was coming in housing, but that we didn't know when or just how bad. FWIW, back in 2012-13, I was reading the same stuff about a Bubble in Student Loans.
He'd have been just as revolutionary to the Republican Party of the 2000s as Bill Clinton was to the Democratic Party of the 1990s.
The Tea Party is butterflied away from this, and it's instead a Liberty or Death party opposed to the economic and social programs. You might even see Trump or Jim Traficant (if he's not convicted) as the Democratic populist backlash/hijacker by 2016.