The national security issue is hurting the Democrats, because they cannot articulate the difference between the 'war on terrorism' and war in general. War in general requires systematically applied violence to depose an enemy army; terrorism is more of an international police problem that requires lots of boring and cooperative work with allies. The Democrats can't explain this difference with logic, they need a symbol, a metaphor to outline the difference. And my guess is that SARS could play that role.
SARS is a medical problem that requires international cooperation through multilateral institutions as well as local intervention in many countries. You can't really hold 'SARS' responsible for its behavior, nor can you impugn the motives of those who suggest ways of tackling the disease. The infrastructure to combat SARS and that to combat bioterrorism are one and the same. More to the point, the consequences of SARS and terrorism are fairly similar, fear of unknown and unpredictable casualties. The prospect of SARS therefore has the ability to change our fundamental outlook on threats from one in which threats are 'evil' and requires high-handed moralism to one in which threats are scientific rational problems, requiring patient cooperative effort to address.
SARS could therefore prove to be an effective symbol of the failure of our bioterrorism and foreign policy strategies, since it's an obviously global problem that must be tackled by international institutions. Linking disease and terrorism as 'borderless threats' moves terrorism away from the poorly constructed 'war on terrorism' framework to one more conducive to a systematic rational response based on international police work.
If terrorism becomes a problem with causes that can be attacked rather than a sort of analytically useless abstraction of evil, the national security issue might shift onto a more progressive framework, as in national security is a problem with a solution rather than a test of patriotic fervor. If the Democrats don't bring this up very soon before we get into flu season, however, they'll just look crassly partisan and cruel.
That said, I really really really really don't want SARS to come back. I sort of enjoy life.