As I wrote this morning, the main thing binding the Lib Dems to the Tories is the promise of a referendum on electoral reform. Should the referendum (expected in spring 2011) be won, the coalition has a decent chance of making it to 2015. But should it be lost, many figures in both parties will expect the coalition to fall apart.
Will there be a Tory-Lib Dem pact at the next election?
The Tories and the Liberal Democrats may agree to support each other under the Alternative Vote.