Last weekend, the White House leaked a copy of a letter sent by President Donald Trump's legal team on Jan. 29 to special counsel Robert Mueller. The letter set forth the president's legal strategy, arguing essentially that he is immune from prosecution for any crime.

To soften the tone of this poorly received letter, the White House dispatched Rudy Giuliani, the president's most visible legal spokesperson, to address the issues that his colleagues had raised. He made matters worse when he suggested that if the president ordered Jim Comey "shot in the Oval Office," he couldn't be prosecuted because the president can pardon himself and because the president's personal and presidential behavior is beyond the reach of the criminal justice system.

Giuliani was supposed to be making a principled case for why the president cannot be subpoenaed to testify before a grand jury, and he ended up discussing absurd hypotheticals about a self-pardon and shooting the former FBI director in the White House.

Here is the back story.

Trump's lawyers' letter argued that obstruction of justice refers to interference with a judicial proceeding and that an FBI investigation is not a judicial proceeding. That was the law before 2002, but an amendment adopted that year provided that any corrupt interference with an FBI investigation that is aimed at producing evidence for a grand jury constitutes obstruction of justice.

The letter's second argument offered that Trump could not have committed obstruction of justice because he controls all that is done in the executive branch and decides what is just, whom to prosecute and whom to overlook. This is the Nixonian argument that "when the president does it, that means that it is not illegal," which was rejected by the lessons of Watergate.

The president is not a king. He took an oath to uphold the Constitution. That includes the rule of law. The rule of law has three unassailable elements. 1) No one is beneath the law's protections. 2) No one is above the law's requirements. 3) No one can be a prosecutor or judge in his own case. The Giuliani argument over the weekend that Trump could have Comey shot in the Oval Office with impunity is not only needlessly tasteless and patently absurd but also contrary to the rule of law, and it is an invitation to presidential lawlessness.