That's part of what the fight over Homeland Security was about
<And it would lessen the one strategic advantage that government has over private business: The government can't get taken to the cleaners by the trial lawyers...
Part of the fight was over just that - an opening to allow trial lawyers to have a shot at the federal treasury. When the federal government helps defray some of the terrorism risk (such as limited liability for a vaccine ordered by the government), it means that lawsuits related to an incident would likely end up being paid by the government. As someone put it, it's Americans suing Americans over a foreign attack.