What if the Federation had backed the Klingon invasion of Cardassia?
Hardliners within the Federation Council are able to win the argument, arguing the Federation's alliance with the Klingons is too important in a time with multiple crisis points and they're able to hold the Council to standing by their Klingon allies providing support and help.
The Klingons effectively conquer the Cardassian Union and put it under occupation. The Maquis become an after-thought and disbands with Cardassian resistance eliminated. On the one hand, it would effectively eliminate Cardassian territory as a future beachhead for the Dominion. On the other hand, the Martok Changeling would still be out there as the head of Klingon forces.
In this scenario, would it have undermined the Changeling's plans and caused them to totally rethink their strategy, or would they have used the Martok Changeling to either cause new conflicts (e.g., have him push to invade Romulan territory next)?