I don’t know, they still seem high. And I don’t know about Nixon, but I heard that Bush, fils, was in the 20s at the end of his term.
http://www.gallup.com/poll/116500/presidential-approval-ratings-george-bush.aspx
George W Bush did hit 25% at low point — at around the 2008 election time, when the Dems hammered him — , but finished higher, at 34%.