Harry Turtledove is the alternate history field's answer to Stephen King, producing a flood of doorstop-sized volumes every year and showing no signs of stopping. One of his notable characteristics is a tendency to take his historical analogies to absurd lengths. Consider, for example, his novel In the Presence of Mine Enemies, set in a world where the Nazis won World War II. Even though the Nazi state has no Cold War rivals (Japan still being an ally), the way the Soviet Union had the United States and the other democracies to compete with in our history, Turtledove has it go through the exact same reform movement as the USSR (albeit with a twenty-year delay).
Nevertheless, I propose to Go Turtledove, and take a historical analogy of my own too far. To be exact, I intend to pursue the idea that the Republican Party has entered a death spiral and, like the Federalist Party before it, is on track to wither into an impotent regional party before finally expiring.
For the purpose of this analogy, I'll assume that Barack Obama's victory over John McCain is analogous to Thomas Jefferson's victory over John Adams in 1800. Like Jefferson and his fellow Democratic-Republicans, Obama and his fellow Democrats have created an unbeatable political coalition. Meanwhile the Republicans, like the Federalists, find themselves with an agenda full of unpopular issues and a shrinking demographic. Obama is now in the same situation as Thomas Jefferson in 1801, in the early days of a generational political dynasty.
If the Federalist analogy holds, then the GOP's demographic disadvantages will continue to result in lost elections in 2010, 2012, and 2014 while Obama wins re-election. Even if Obama screws up as badly as Jefferson did with the Embargo Act of 1807, the Republicans' lack of organization outside their Southern base will not allow them to regain a majority in Congress. The 2016 presidential election will see the victory of Democratic candidate Senator Sheldon Whitehouse* and further Republican losses in Congress. This will be repeated in 2024 with the election of the third Democratic president in a row, Senator Robin Carnahan, accompanied by Democratic supermajorities in both houses of Congress.
By the time of the 2028 election, dissatisfaction with their permanent minority status will cause the Republicans' Congressional caucuses to fragment. Likewise, growing ideological conflicts within the Democratic Party will result in a party split in 2032, with several factions running their own independent presidential candidates. This will throw the election to the House of Representatives, where horse-trading will result in the candidate with the popular vote plurality failing to win the election. This split will solidify into a new set of political parties, with the popular but unelected candidate of 2032 finally winning election in 2036. The remaining fragments of the Republican Party will be absorbed into one or the other of the newly-formed parties, and the Party of Lincoln will be no more.
*Remember, folks, you heard it here first!