Barack Obama, mindful of the urgent power of a president’s words, liked to say he was guarded with his language because anything he said could send troops marching or markets tumbling.

His successor, Donald Trump, showed no such restraint.

Now Trump is facing dozens of criminal charges in four separate indictments, two ofthem anchored in the Republican’s lie that he did not lose the 2020 presidential election to Democrat Joe Biden. And Trump’s propensity for falsehoods and his right to utter them are at the core of his legal defense.

Though the U.S. presidency is vested with many overt powers, one of the most important is implicit — the power of rhetoric. It is used often as a call to action, to rally Americans for a mission abroad, to comfort a grieving public after tragedy or to sacrifice for a greater good.

“Scholars like me who study presidential rhetoric, presidential communication, they call it essentially a second Constitution,” said Jennifer Mercieca, a communications scholar at Texas A&M University. Having presidents communicate directly to the public “changed the complete balance and separation of powers without having a new constitutional convention. It made the president the center of our political system.”

Trump, in effect, is arguing that his words as president carried no special force and he was simply exercising his free speech rights.

“Most presidents have a sense of the importance of language — of the written word, of the spoken word,” said Wayne Fields, a professor at Washington University in St. Louis and an expert on presidential rhetoric. “Some of them are not particularly good at it themselves, but they rarely are quite so dismissive of it as Trump has been.”

Lawyers for the former president, who now is facing criminal charges in courtrooms stretching from Miami to New York, have made clear that Trump’s free speech rights will form the foundation of their defense in the Jan. 6 case. John Lauro, one of the lawyers, characterized to CNN that special counsel Jack Smith’s case was “very, very unusual, outside-of-the-bounds criminal prosecution of First Amendment rights.”