And what does this have to do with the price of tape recorders in Red China? The prime minister is answerable to the will of parliament 24/7. In the US Congress, if the Congress does not want to initiate impeachment procecedures, no matter how egregious the crime, the President still walks. The Republicans in the House, they have the majority, they could block any   impeachment procedures.
Impeachment has nothing to do with the Mueller investigation.