As far as I can, the US laws allow new parties to form. The trouble is the strategic voting syndrome. Today a vote for the Green Party is almost as good as a vote for the Republican Party: a green vote takes one vote away from the D's. In 1992, a vote for Ross Perot was a vote for Bill Clinton.

New parties can form, but the hegemony of the D's and R's is still there.

The US needs to get rid of its entire constitution. It's time to build a new one.