Mike Sances has a great post, accompanied by charts, showing that declining trust in government over the last several decades has resulted in large part from partisanship. People have grown far less likely to trust government when the other party controls the White House:
You can intuitively see that Republicans trust government during GOP presidencies but not Democratic presidencies, and the reverse as well, and that this has grown increasingly true. Here he pulls out the partisan gap:
Partisanship is not the whole story. In the early 1960s, everybody trusted the government. Now, even when their party controls the White House, neither side trusts the government as much as everybody did fifty years ago. Still, polarization is a big part of the story.