Rasmussen has him at 50% approval today. Both those things cannot be true.
Probably, like in everything else, support for impeachment is over 40% and opposition to impeachment is over 40% with a gray area in the middle - anybody's guess.
Also it depends on how they ask the question and what people understand by "impeachment."
What's striking is that not many people are saying "I disapprove of him but don't think he should be impeached." That middle ground isn't very big.