[acdha]

Several people have already mentioned the risks of MITM on a .gov domain. In this case, I think it goes beyond the usual risk of injecting malware / etc. on a trustworthy domain because it'd make an interesting watering hole attack because some of the visitors to senate.gov are going to be people with interesting information or access both on their computers and via their social networks.

Imagine if, say, a foreign intelligence agency managed to compromise some routers, do some DNS poisoning, etc. in the DC area and, being professionals, instead of injecting adware they inject a quiet zero-day which scrapes network info, contacts, etc. and reports home. Some of that will be political junkies, kids working on school reports, etc. but I'm sure you'd also get access to clients at a bunch of interesting agencies, NGOs, etc. which would be helpful for more targeted attacks.