Every cloud has a silver lining

From WaPo:

The recent collapse on Wall Street appears to have found another victim: the independent political groups aiming to make an impact on the 2008 elections.

Expected to be a force in the final weeks of the presidential race, outside groups and the pointed advertising they brought to the airwaves in recent campaigns are barely evident this year. Political operatives say the fact that many wealthy potential donors have shied away from investing in efforts such as the infamous Swift Boat Veterans for Truth is that they are simply too busy trying to salvage their own financial portfolios.

I believe the phrase you're looking for is 'hoist on their own petard'.