No Terror Alerts Since Election Day? Hmmmm!

A good question is raised by Josh Marshal at Talking Points Memo:

When was the last time there was a major terror alert? They were something like a regular occurence for the eighteen months or so before the 2004 election. And through 2004 the administration pushed the line that al Qaida was aiming to disrupt the elections themselves. But as near I can tell there hasn't been a single one since election day.

Through 2004, of course, critics of the administration routinely questioned whether the frequency and timing of the various terror alerts were not all or in part for political effect.

How do we explain what appears to be a night and day difference between the year prior to November 2004 and the year since in terms of terror alerts and scares?