Here are the facts:

On Thursday, two days before the march, the military conducted some sort of top secret exercise in the DC area.

Bush and others cleared out of DC for the weekend.

The CDC has found tularemia in filters placed around the Mall on Sept 24 and 25.

The US military has a long, sordid history of using US citizens for secret testing of bioweapons.

The military has been working with tularemia for some time as a biological weapon.

Here is the speculation:

The military wanted to test tularemia as a bio-weapon. It knew that a whole bunch of people would be in DC and that the administration would not miss any of them. So, on Thursday it places tularemia in delivery systemns. No idea which system was chosen, but a simple one would be in the ground where it would be stirred up by people marching/walking in mass numbers on Saturday.

Since the military does not really want to kill people, just see how many people get exposed to the bug and of them how many people get sick, it is crucial to spread the word ASAP about the exposure so that people will rush to their doctors for testing. Therefore, the fact that the CDC has filters in place to detect the bug is important. The news of the tularemia is quickly disseminated on TV, newspapers and on the internet at sites like this one. The CDC tells everyone to hurry to the doctors for blood tests if they show any systems of possible disease.

Result, free clinical trial for the military of the effectiveness of whatever delivery system they chose to test out on a population that they despise.