Conservative former federal judge J. Michael Luttig on Monday sounded the alarm over Donald Trump’s recent remark that he doesn’t know if he is obligated to uphold the U.S. Constitution, calling it “perhaps the most important words ever spoken by a president of the United States.”

Luttig, a longtime critic of Trump’s anti-democratic rhetoric, told MSNBC’s Nicolle Wallace: “The president always says what’s on his mind with almost perfect clarity of what is on his mind. Now, sometimes what’s on his mind is confusing, but the words that he chooses are perfectly clear as to his confusion.”

He continued: “The temptation here is to dismiss the president’s words as just another gaffe, of which he makes many. But I don’t think that we should do that. I’m quite confident that the president was saying what is on his mind and that is that he, the president of the United States, doesn’t necessarily believe that he is obligated to uphold the Constitution of the United States, as it is interpreted by the Supreme Court.”

Luttig characterized Trump’s statement as a form of “constitutional denialism,” the school of thought that argues the Constitution doesn’t mean what the Supreme Court interprets it to be.

What Trump believes about his obligation to uphold the Constitution “is one of, if not the single most important issue of our times,” Luttig concluded.