Adrian Vermeule has posted a very interesting essay on SSRN: Emergency Lawmaking After 9/11 and 7/7. The argument:

This essay offers case studies of three emergency statutes, all dealing with terrorism and all enacted within less than a year after a major terrorist attack: the September 14, 2001 Authorization to Use Military Force; the USA PATRIOT Act; and the U.K. Terrorism Act 2006. A standard worry about such cases is that the circumstances of emergency lawmaking produce blank-check delegations to the executive. The fog of uncertainty, emotions such as urgency and visceral fear, and the tendency of legislators and the public to rally 'round the flag, all cause legislators to vote the executive massive new powers, regardless of whether those powers are rationally justifiable. This view is descriptively and theoretically flawed. Descriptively, executives in all three episodes lost control of the political dynamics, faced bipartisan resistance or rebellion in the legislature, and ended up obtaining far less than they asked for or desired. Theoretically, emergency conditions have cross-cutting political effects on legislators. The mechanisms and forces operative during emergency lawmaking cut both ways, constraining as well as empowering the executive, with unpredictable net results in particular cases. Although executives usually receive new powers in emergencies, there is no reason to think that they systematically tend to receive more new authority than a rational legislature would provide.

  I think that's plausible, and it seems correct to me in the case of the Patriot Act in particular.

  There's also a second-order dynamic here. Emergency legislation creates fear of overreaching that often leads to later legislation tempering the more controversial aspects of the emergency legislation. For example, the Patriot Act renewal legislation in 2006 added privacy protections to counter fears of certain provisions of the Patriot Act. And right now, Congress is considering legislation adding protections to counter fears of certain provisions enacted by the Protect America Act of 2007 (the FISA legislation pass a few months ago).

  Thanks to Larry Solum for the link.