The US is essentially a zero party system. Passing laws in the senate requires 2/3 of the votes with usually means that politicians from both parties have to support the legislation.

Not true; laws can pass with as few as 1/2 of the votes (51). However, this is increased to 60 if the opposing side chooses to filibuster (which non-selectively blocks all legislation), and it's increased to 2/3 if the President chooses to veto it. Use of the filibuster was rare before Obama came into office, at which point the Republican party adopted a policy of using it constantly.