I have been talking a lot about Delta's west coast expansion on Uprd.com, and looked specifically at their west coat flights/announcements yesterday. DL is attacking AS in more than just Seattle. But also LAX & PDX.

The Problem is DL is still using AS a lot to feed international flights from Seattle to smaller markets in/around the PNW where DL currently doesn't serve, but Horizon does. In addition, AS has frequency that DL does not offer on North-West routes.

AA does not have the market presence in Seattle that DL has, and their corner stone strategy would require AS to feed LAX where AS has a decent build up, but nothing like SEA.

Could DL survive in Seattle without AS? I'm not sure. But if AS/AA team up and coordinate routes better, it could hurt DL in the end, especially if AS ends their DL partnership before all these west coast flights officially launch