Neither of these proposals is satisfactory. The legislative solution goes too far: The president’s exclusive constitutional authority to hire and fire executive branch officials charged with implementing his core Article II duty to “take Care that the Laws be faithfully executed” cannot be divided without working long-term mischief to our constitutional structure, as Justice Scalia eloquently explained nearly 30 years ago. Our system is designed to leave that power in the hands of the president, and to impose the costs of its misuse through the political process (elections, impeachment, Congress withholding funds, etc.), not the judicial system. The courts are too powerful already to take a central congressional oversight function over a central presidential power and delegate it to three life-tenured judges, so that if the voters are dissatisfied, they have nobody to blame.
On the other hand, restraining Trump with a threat that the Republican-controlled Congress might impeach him is too weak. True, the need to work with Republicans has disciplined Trump more than commonly thought, in ways ranging from McGahn’s dissuading him from firing Mueller to Trump’s endorsing Mitch McConnell’s preferred candidate in the Alabama Senate primary. But on the whole, Trump knows full well that the Republican Congress’s own voter base still doesn’t want him impeached and is more likely to punish them for being too hard on Trump than too lenient. Some Republicans, especially in the Senate, would be ready to impose real punishments on Trump if he sacked Mueller, but from where Trump sits right now, it looks like an empty threat to get enough on board to pull the trigger.