End of the Republican era
Today's election is poised to end the Republican era in American politics - an era that began in reaction to Lyndon Johnson's Great Society, the Vietnam war and the civil rights revolution, was pioneered by Richard Nixon, consolidated by Ronald Reagan, and wrecked by George W Bush.
Almost every aspect of the Republican ascendancy has been discredited and lies in tatters - its policies, politics, and even its version of patriotism - down to the rock-bottom notion that progressive taxation itself, initiated by a Republican president, Theodore Roosevelt, who John McCain hails as his personal icon, is unpatriotic.
Now, certain factors that have dominated US politics for 40 years seem destined to recede to the far corners. In economics, supply-side panaceas and deregulation created the worst crisis since the Great Depression, requiring a conservative Republican administration to part-nationalise banks, something unimaginable under any Democratic administration. In foreign policy, neoconservatism led to the morass in Iraq and Afghanistan while undermining the western alliance. In social policy, the evangelical right battered science, the separation of church and state, and the right to privacy. Finally, the conservative principle of limited government has become a watchword for incompetence, cronyism, corruption, hypocrisy, and contempt for the rule of law.
Really, read the whole thing. It hits both the macro level of decades of history, and the micro level of the campaign itself.