This is from an Associate Press article I saw on Yahoo:
Johnson, Reagan and Clinton also slipped into the mid-to-high 30s at some point during their terms. Truman, Nixon, Carter and George H.W. Bush saw their numbers slump into the 20s, with Truman's at one point dipping to 23 percent.
On Washington Week last night one of the reporters said that Bush has a negative approval rating of up to 45% in some New England states. Bush hasn't fallen his hard since his last bike ride.
Even if Bush's floor doesn't get much lower, his disapprovals could get much higher, especially in the South, which supplies 40% of our recruits.
During MonicaGate, Clinton's approvals never fell below 55% and got as high as 70%. From the same AP article:
Clinton proposed an ambitious agenda in his 1998 State of the Union address, a week after an investigation began into his relationship with White House intern Lewinsky. He traveled extensively. And his approval ratings rose to as high as 70 percent even as the Republican-controlled House voted to impeach him.