Many highway projects, and more recently HSR, are make work projects for unions and favored contractors. If the TEA Party succeeds in reducing spending there should be less money and an appetite to fund expansion of non essential infrastructure instead of maintaining what is already built.
Defense spending is a whole other issue. Contractors are overcharging the government, procurement is a mess, and many officials have been using defense projects as make work projects for their home states. Vital replacement of worn out equipment was getting deferred during the Clinton years in favor of make work projects. When the shooting wars started, most of the pork remained as the budget was upped for emergency replacement of vital equipment.
There's also a huge excess of senior leadership left over from the WWII mentality of needing extra officers to quickly lead a large conscripted army in case of a World War. With an all volunteer army and large reserves of professionally trained people, there's no need for all the expensive desk jockies to be sitting around anymore. Especially whereas they are expensive, draw large benefits, and greatly contribute to the procurement mess.
It also doesn't help that we are staging troops in areas they are no longer needed at insanely high costs. If most of peaceful world wants our defense umbrella they should be paying us for protection rather than having us foot their defense bill. There are strategic exceptions and the Navy requires overseas basing to protect shipping interests, however we must stop subsidizing other countries defense and paying them leases to do so.
With significant reform defense spending could probably be cut 20-25% for an actually MORE effective military. The problem is getting all the fat trimmed out of the hamburger. An across the top cut would devastate the military's effectiveness without addressing the gross inefficiency of spending issues.
I honestly expect the country is eventually going to default or at least get very close to it. Followed by a period of austerity which sees the government dramatically reigned, by shear force of the economic reality, in to pre-New Deal size and public sector unions abolished. There'll probably be a dramatic fear of inflation, similar to what's in Germany, and an absolute paranoia about ever letting the government get to a large enough size, with a big enough spending capacity, to cause another default.
Did I mention we are boned?