Even if Trump fires him, Mueller could have plenty to say
Congress could require that, if the special counsel is fired, he report to the House and Senate the status of his investigation as of the date of dismissal, with specific attention to any evidence of criminal activity that implicates the president. As part of this measure, Mueller would have to note the existence of evidence protected by grand-jury secrecy rules, enabling Congress to take legal action to obtain it.
.. This reporting requirement would prevent the president from denying Congress access to evidence that bears on the exercise of its impeachment power. It may also give the president some pause in proceeding with a dismissal.
.. If the firing were genuinely for good cause, without corrupt purpose of self-protection, the president should have nothing to fear from this disclosure to Congress.
.. His firing would trigger a straightforward obligation to advise Congress of findings pertaining to presidential misconduct. In effect, the report would mark the beginning of the investigation. It would not supplant it.
This measure should be hard to oppose.
.. Of course, if a bill to protect the special counsel passed, the president could veto it, but his action would speak volumes about his intent to keep open the option of firing Mueller and burying the product of his investigation. Regardless of whether Congress would override his veto, it would be a fateful moment in this presidency.
.. In providing by law that Mueller, if fired, will report on any evidence of presidential misconduct, Congress will accomplish at once two goals: signaling to the president that it is alert to the possibility of obstruction of justice masquerading as disciplinary action, and assuring the preservation of evidence relevant to an inquiry into grounds for impeachment.