Borderline Truthiness
But politics isn't social science, where causality must be rigorously proven. Politics is, to be blunt, whatever you can get away with saying to the voters. Think not B.F. Skinner, but rather P.T. Barnum, in other words. "Event X happened because party Y passed legislation Z" is an expected statement from a politician, on any subject under the sun. Call it "spin" if you will, but a large part of it lies in convincing the American public that you have a right to claim credit because of your policies.