The Epoch Times had a good chart showing what the federal government projected it would do with our taxes in 2007:
Social Security is the largest outlay, with 21% of our taxes going there. Next up is Defense, with 19%. Obama may reduce defense spending to shift more taxes towards infrastructure spending. Doing it this way would allow him not to raise taxes.
Defense hawks may disagree with any decrease in defense spending, arguing that it would cause a decline in domestic security. I do believe terrorists will hit the United States again, but much of the current defense spending is on major projects, like stealth fighters. Meanwhile, port security is inadequate. Consider this simple, low-tech scenario: a terrorist pays two dock workers to put an unmarked package on a ship. The dock workers will be told they are transporting drugs and will be paid a few thousand dollars for their discretion. In reality, the box would contain a major bomb or chemical weapon. The bomb doesn't even have to be inside a box. The terrorists could place a bomb inside an imported car, major appliance, or some other product that has many electrical components, making the bomb harder to detect.
Rather than focus on large-scale projects, such as the next generation of aircraft, which always seem to run over cost, the U.S. should shift more money into intelligence work. More specifically, Obama should hire more workers to 1) supervise America's major ports (e.g., Los Angeles, Miami, etc.); and 2) more effectively monitor the contents of packages before ships on-load and offload them. I realize modern ports have automated systems, but having more hi-tech automation doesn't necessarily lead to higher security.
If you're interested in reading more about Obama and defense spending, here is an interesting article: