The chart above was created by Jeff Dobbs, and it shows an interesting correlation between Congressional approval numbers and the number of Republicans in the Senate.
I say correlation, because nothing hear establishes that Republicans in the Senate are necessary the cause of the fluctuations in approval.
For one thing, Congress is more than just the Senate. There is the House as well, and the agenda of whoever is President at the time weighs heavily on what Congress does, especially depending on whether or not the President is of the party controlling Congress. The approval of Congress can be as reflective of the President’s agenda as it can be of Congressional performance.
Would putting Republicans back in charge of the Senate, and thus all of Congress (assuming the keep the House in 2014, which seems extremely likely), make Congress more popular? A Republican Congress and a Democrat president might turn the trick.
Looking at the chart, the high water mark for Congressional approval in the last 25 years came during the latter Clinton years when he squared off with a Republican Congress.