The best case: This is an example of America's democratic institutions reasserting themselves in the face of the attempt by a panicked technocratic elite to prop up reckless institutions that richly deserve to fail.
The worst case: You know what.
The most likely scenario, as of 3 PM this afternoon: The stock market continues to drop. Some version of the bailout passes in the next week. The American economy staggers into a recession, but passes through the storm without 1930s-style suffering; the Republican Party is not so fortunate. Even though most Americans claim to oppose the bailout [update: not anymore], the House GOP's obstructionism is widely viewed as having worsened the economic situation; the fact that these are contradictory positions does not faze an electorate that wraps all of the country's current troubles up, ties them with a bow, and lays them at the feet of the Bush-led GOP. John McCain loses by a landslide in November. The Democratic Party regains years or even decades worth of ground among the white working class, consolidates the Hispanic vote, and locks up a large chunk of highly-educated voters who might otherwise lean conservative. The much-discussed liberal realignment happens. And a politician running on a Ron Paul-style economic platform does very, very well in the GOP primaries of 2012.