My prediction is that after the death of the Democratic Party, the GOP will go through a period of hegemony, and will take a turn to populism, as can be seen now with Bush's version of Hillarycare, no Children Left Behing, and other "jems", proposed by a president who was supposed to be a conservative.
Than, the Libertarian party will emerge because it will hold the diametricaly oppost position of the new republican party, and some figures of the GOP will join the LP.
It only takes a shift in the political axis from Liberal-Conservative, to Populist-Libertarian.
I think this would be especially fascinating, as it would leave the GOP occupying pretty much the same political space that the Democrats occupied at the start of the 20th Century.
