ABC News has this story about the 2012 presidential election, and alternatives to the two major parties. Like many other stories, this story quotes an authority who says that if someone were elected President who wasn’t the nominee of either of the two major parties, that person would not be able to work with Congress. In this case the quoted authority is Professor Jonathan Ladd.
It is surprising that people who make this point never seem to remember that the U.S. has had six minor party or independent Governors elected in the last 40 years (two in Maine, and one each in Minnesota, Alaska, Connecticut, and Rhode Island), and that these Governors did work with their state legislatures and did get things done.