Call it an unwritten rule — a matter of decorum among the small fraternity of men who once held the title "leader of the free world."
Before he left office, Barack Obama said his goal was to steer clear of the political spotlight — as George W. Bush had done when he left the White House — giving the new president room to govern without Obama's shouldering into every debate with the megaphone that being a former commander in chief affords.
But a Fox Business commentator said Obama violated that unwritten rule with a recent comment about Trump's tweets. What's more, according to Fox Business host Lou Dobbs, that violation should merit arrest.
"I think U.S. marshals should follow [Obama], and anytime he wants to go follow the president like he is and behave [like that]," Dobbs said on his show Friday. "I mean, this is just bad manners. It's boorish and it's absurd and he doesn't realize how foolish he looks."
"I mean, he should be brought back by the marshals. Isn't there some law that says presidents shouldn't be attacking sitting presidents?"
The Obama comments in question came during a leadership forum in India, according to The Washington Post's Annie Gowen.
Someone asked Obama about recent comments made by his wife, Michelle, in Toronto: The former first lady said it was never a good idea to "tweet from bed," a not-so-subtle commentary on Trump's early-morning social media habits.
In New Delhi, her husband agreed.
"Michelle was giving the general idea. . . . Don't say the first thing that pops in your head. Have a little bit of an edit function," he said. "Think before you speak. Think before you tweet."
Telling Trump to have an edit function is far from the worst thing a former president has said about the commander in chief.
Obama has made stronger statements while defending his legacy against Trump's attempts to repeal the Affordable Care Act, end the United States' participation in the Paris climate accord and impose stricter immigration limits.
In January, according to The Post's Juliet Eilperin, Obama encouraged Americans to protest Trump's move to ban citizens from seven majority-Muslim countries from entering the United States.
"The President fundamentally disagrees with the notion of discriminating against individuals because of their faith or religion," Obama spokesman Kevin Lewis said in a statement.
Obama is not the only president to criticize Trump. According to The Post's David Nakamura, during a rare political speech, former president George W. Bush criticized a political system "corrupted by conspiracy theories and outright fabrication" in which nationalism has been "distorted into nativism."
"We've seen our discourse degraded by casual cruelty," Bush said during a 16-minute address at "The Spirit of Liberty" event. "Bullying and prejudice in our public life sets a national tone and provides permission for cruelty and bigotry. The only way to pass along civic values is to first live up to them."
Bush's father, the 41st president, bashed Trump in more concise, plainer terms, according to CNN.
In historian Mark Updegrove's new book, titled "The Last Republicans," George H.W. Bush said of Trump: "He's a blowhard."
"This guy doesn't know what it means to be president."
By Dobbs' reasoning, the marshals may also have to come for the Bushes, too.