Merrick Garland must investigate Donald Trump’s attempted coup — not for retribution but for deterrence

With increasing and troubling frequency, an argument is being made that former presidents should be presumptively shielded from criminal investigation and prosecution unless it is all but certain that a jury would return a conviction — a much higher bar than applies to anyone else. The argument amounts to a claim that — regardless of the nature of the crime — a former president should be above the law and beyond its reach. It’s one thing to debate the case-by-case wisdom of prosecuting a sitting or former president. It’s another to let that debate bring about the...