Sometimes politics is subtle.And then there are days like today.Sitting in the Press Gallery, watching Prime Minister’s Questions this lunchtime, you could feel, hear and smell Boris Johnson’s authority draining away.The faces and demeanour of Conservative MPs. His backbenchers sat there in near silence.All the noise came from the opposition benches. It was Mr Johnson’s toughest PMQs he’s faced since the general election.And it’s only lunchtime.