After his impeachment proceedings in 1998 and 1999, Bill Clinton's rating reached its highest point at 73% approval. He finished with a Gallup poll approval rating of 65%, higher than that of every other departing president measured since Harry Truman.
The reason that Clinton’s poll numbers improved was because the public did not believe that the president’s personal life, no matter how salacious, was sufficient reason for impeachment. It was the Republicans who ended up paying the price, especially Bob Livingston and Newt Gingrich.
This time the Republicans only have allegations but no evidence. There is no semen stained blue dress, “perfect phone call” or a riot egged on by the president.