Here is a good test for us all. Imagine that Obama  was the one in Trump's shoes and fired the Head of the FBI leading an investigation of him. Further, assume Obama had dinner with the Head of the FBI seeking reappointment and it is alleged (not proven) that Obama asked for a pledge of loyalty and asked if he was under investigation. I think that the Republicans would move to impeach Obama (and rightfully so). The charge would be Obama's offering or accepting a bribe which under the constitution calls for impeachment. The Obama bribe is a job for a pledge of loyalty and assurance Obama is not under investigation or a Obama's acceptance of a bribe of loyalty and assurance re investigation for a job. There would be an investigation as a result (the President cannot be charged for a crime then investigated, but must be impeached by Congress then investigated). Think about that.