There can be little doubt that Mr. Trump views the Justice Department as a tool to punish his political enemies and give his allies a free pass. He has also made it clear that he hates “rats,” praising the felon, Paul Manafort, who once ran his campaign for refusing to “break” by cooperating with law enforcement.

This is our new normal, and congressional Republicans have made it clear through their inaction that they will not remove Mr. Trump from office for obstruction of justice. That matters because the Justice Department has long concluded that a sitting president cannot be indicted (although for many legal scholars, that remains an open question). Mr. Mueller is likely to follow that guidance and submit a report to Congress instead of indicting the president for obstructing justice.

It is hard to imagine 19 Republican Senators voting to convict Mr. Trump for obstructing justice. In itself, that does not mean his presidency will survive until 2020 (or beyond), given the array of legal problems he now faces. After all, just two weeks ago, his former lawyer, Michael Cohen, told a judge under oath that Mr. Trump directed him to commit crimes. But obstruction appears to be the first existential challenge to the Trump presidency if reports that Mr. Mueller is preparing a report regarding obstruction are accurate.