There were rublings from day 1 due to not being Corbyn. It has gotten louder in the last month though.

His problem will be the same for any other leader though. Nothing sticks to Johnson he can successfully land the blows at the dispatch box. Occasionally it's makes a minor dent in the polls then it resets back to where it was.

Until something does stick or a change in PM can't see anyone else doing better or worse.