Or maybe disarm the population a little so that police don't feel like they're in an arms race?
We cannot disarm the population by fiat, because the Supreme Court has held that the 2nd Amendment provides an individual right to bear firearms. Changing that would require radically altering either the composition of the Supreme Court, or the text of the Constitution.
Still, less guns on both sides seems more likely to succeed than disarming only the police.
The problem is, in the United States, you can't reduce the number of guns in civilian hands. But you can reduce the number of guns in the hands of the police. Strange, but true.