No matter how “phony” Obama may believe the Benghazi, IRS, (etc. etc. etc.) scandals are or how biased his lapdog media is in reporting on them, the American public can tell that Democrats are doing a crap job in Washington.
Before the federal government can pass a law, it must be passed by both the House of Representatives and the Senate, then signed by the President. At any given time, 2/3 or 3/3 are controlled by either Republicans or Democrats. The dominant controlling party obviously has the most power over what laws get passed and thus bears the majority of the responsibility for how well the government serves the people.
As you can see from this graphic, trust in government has been strongly correlated with which party this is. When Democrats have been in control, trust has fallen and distrust has risen. When Republicans have been in control, the opposite has been true.
Note: The dominant 2/3 or 3/3 party is in pale colors under the poll results. The breakdown is in dark colors at the bottom.