There would have to be some fundamental changes in political reality -- most notably that America has become an outright dictatorship. One would have to start with the elections of 2006 that in real life brought huge losses to the Republican Party but in this reality brought ral gains.
So the GOP would have to have made gains in the House instead of huge losses, that GOP incumbents won re-election, that GOP Senate incumbents (except for Lincoln Chaffee, defeated in the primaries by a hard-line GOP challenger who subsequently wins) win, and that the GOP actually wins the governorship of Ohio (rewarding Kenneth Blackwell for arranging a first re-election for Dubya) and a couple of Senate seats in Michigan and New Jersey.
Ratification of the 28th Amendment takes place in a climate of terror, but the Democrats still exist and play by the new rules. The rules are that the Opposition shows up at debates but that the Ruling party controls the polls where things matter. Mainstream news media compete to praise the Great and Glorious Leader who must bring America through dangerous times. The times are dangerous, and the media tell Americans that the economic recession proves the need for GOP leadership on the economy -- tax cuts for the super-rich, business subsidies, and tax shifts to the non-rich, an abolition of the minimum wage laws, and all sorts of goodies. Bush can run for a third term, and he wins in a landslide, picking up everything but D.C., Maryland, Rhode Island, Massachusetts, Vermont, and Hawaii.
Real power has of course gone to the leadership of the Party Apparatus, and political decisions are really made at the Party Conventions.
Great scenario !
In a non-dictatorial scenario ( but you're right, that's almost impossible ), Kerry would have destroyed Bush :