He might have to take $1

The president of the United States stands to make $400,000 every year, but Donald Trump wants none of it.

"As far as salary is concerned, I won't take even one dollar," Trump said in a Q&A Twitter session in September 2015. "I am totally giving up my salary if I become president."

Trump reiterated this pledge as president-elect more than a year later on Nov. 13, 2016, when he told 60 Minutes' Lesley Stahl he still wouldn't take the salary.

"I think I have to by law take $1, so I'll take $1 a year," Trump said. "But it's a ― I don't even know what it is. Do you know what the salary is?"

"$400,000 you're giving up," Stahl said.

"No, I'm not gonna take the salary," Trump responded. "I'm not taking it."

WHY HE'S PROMISING IT

Trump's pledge is similar to the precedent set by John F. Kennedy and Herbert Hoover, who donated their presidential salaries to charitable causes. Both men were wealthy prior to their presidency.

Discussions about the president's salary trace back as far as 1789.

According to congressional records, George Washington initially declined his $25,000 salary, but Congress refused to comply. Congress didn't do this for the president's benefit, but did so to encourage financial independence and prevent the president from being bribed by outside incentives.

WHAT NEEDS TO HAPPEN

Trump has a few options if he chooses to decline his salary.

He could donate his salary like past presidents or he could give his salary back to the U.S. Department of Treasury, said Michael McConnell, the director of Constitutional Law Center at Stanford University.

Whether he could flat-out reject his salary or just take $1 is a complicated question.

Article II, Sec. 1, Clause 7 of the Constitution prescribes a president be paid compensation "which shall neither be increased nor diminished during the period for which he shall have been elected, and he shall not receive within that period any other emolument from the United States, or any of them."

WHAT'S STANDING IN HIS WAY

As of September 2016, Forbes estimated Trump's worth at about $3.7 billion, meaning Trump could definitely afford to forgo his salary.

The only other problem that could come up is if Trump tries to flat-out reject the salary. There has been no precedent for this, so experts are uncertain whether he is legally obligated to take his salary.