Does anyone find it odd that Starfleet happens to moblize a fleet to take Torros and combat the pending Dominion invasion of 2373 AND repel the Borg incursion of Sector 001 AT THE SAME TIME?
Surely the Dominion was aware of the Borg's presence and picked such a ripe time to attack. I theorize their heads have bumped before, and the Dominion is still standing :-D!
As pointed out above they didn't happen at the same time. Plus Starfleet is large enough and powerful enough that it can defend an empire 8,000ly wide so it should be able to fight off a lone attack and then compete in a wider war.
Also the Dominion War didn't start at the Dominion's choosing, it was forced onto them by the Federation when they mined the wormhole.