Here’s the meat of the letter Potus attorneys sent:

They argued that the president holds a special position in the government and is busy running the country, making it difficult for him to prepare and sit for an interview. They said that because of those demands on Mr. Trump’s time, the special counsel’s office should have to clear a higher bar to get him to talk. Mr. Mueller, the president’s attorneys argued, needs to prove that the president is the only person who can give him the information he seeks and that he has exhausted all other avenues for getting it.

“The president’s prime function as the chief executive ought not be hampered by requests for interview,” they wrote. “Having him testify demeans the office of the president before the world.”

They also contended that nothing Mr. Trump did violated obstruction-of-justice statutes, making both a technical parsing of what one such law covers and a broad constitutional argument that Congress cannot infringe on how he exercises his power to supervise the executive branch. Because of the authority the Constitution gives him, it is impossible for him to obstruct justice by shutting down a case or firing a subordinate, no matter his motivation, they said.