The Melania controversy is nothing new: Eleanor Roosevelt pitched hot dog buns

The tall, regal first lady was a magnet for marketers – and she happily signed on. During her years in the White House, she became a paid pitchwoman for hot dog buns, mattresses and air travel.

Many Americans were aghast at the sight of the president's wife lending her name and face to hawk products in commercial advertising; Congress launched an investigation. But the controversy died down when Eleanor Roosevelt disclosed that she had donated most of her earnings to charity.

A similar round of pearl-clutching erupted in Washington this week when Melania Trump's lawyers argued in a libel lawsuit that a British tabloid's sleazy accusations about her past had damaged her chances to capitalize on "multimillion dollar business relationships" at a time when she was "one of the most photographed women in the world."

The East Wing as a marketing opportunity? Trump's representatives later issued indignant denials, saying she "has no intention" of trying to profit from her role. (The defamatory story was published in August, at a time when few expected the Trumps to take the White House, and the former model had once had a sideline selling "Melania" jewelry.)

But her lawsuit revealed an unspoken truth: Modern first ladies know that inherent to the role is the power to sell.

[Melania Trump settles defamation claim against blogger]

Roosevelt showed up in print and television commercials endorsing bread products, margarine and even the burgeoning airline industry. The latter featured a portrait of Roosevelt seated on a plane, serenely knitting above this quote: "I never cease to marvel at the airplane." Roosevelt was surprised at her ability to push products, historians recalled, but in the years since the selling power of first ladies has been well documented.

Their position is unsalaried and the work is unofficial, but presidents' wives have used their platforms to promote worthy causes, promote their husbands – and, sometimes, promote themselves.

Lady Bird Johnson, now seen as a pioneering environmentalist, led a nationwide campaign to discourage roadside littering. Michelle Obama produced public service announcements encouraging children to eat their vegetables, at the same time her husband attempted to overhaul the nation's health care system. Nancy Reagan launched her "just say no" campaign to steer kids away from substance abuse that dovetailed with her husband's war on drugs.

Of course, these were all pursuits with the public interest in mind, and none stood to gain personally from this kind of promotional work.

And all first ladies have sought to sell the nation on the likability of their husbands – as Melania did in interviews during Donald Trump's campaign for president when she spoke of "the Donald only I know."

(Even when they're not trying, first ladies can be startlingly effective at selling commercial goods. A study in the Harvard Business Review found Obama boosted the stock-prices of the fashion brands she wore significantly, creating tens of millions of dollars in value.)

Though the new first lady has been slow to set up a staff or embrace the public aspects of her role, she is uniquely suited for some aspects of it. She worked as a model, essentially a walking advertisement for fashion designers, then later hawked her eponymous jewelry collection on the television network QVC – an accomplishment touted by the White House website, though her official bio dropped mention of the home shopping channel.

Celebrity branding expert Jeetendr Sehdev sees the potential for creating of a commercial enterprise around the first lady as just another marketing opportunity in a culture rife with them.

"She would be redefining what it means to be a first lady, and there would be people who loved it, who would see it as a game-changer, and there would be people who would hate it," he said.

Well, yes: Some people would understandably hate it, since it is technically illegal for a president or his spouse to profit off the presidency.

The Trumps have already run into ethical quandaries around their family business, including a PR pitch by Ivanka Trump Fine Jewelry calling attention to a $10,800 bracelet she wore during an interview following her father's election. Ivanka Trump vowed to sever ties with her business soon after.

Still, the idea of the first lady as a brand is not unheard of – though it is rarely spoken of in such frank terms.

During the early days of the Obama White House, social secretary Desirée Rogers referred to the "Obama brand" in a luxury magazine and was promptly smacked down. "The president is a person not a product," senior adviser David Axlerod reportedly told her.

Indeed, Roosevelt faced "unrelenting fury" when she allowed her literary and talent agents sell her image and name to advertise products, said Carl Sferrazza Anthony, a historian for the National First Ladies Library in Canton, Ohio.

"It wasn't just that she was seen as making money off the presidency but that by promoting a product she was also somehow degrading the dignity of the presidency," he said.

The closest any member of a first family came to replicating Roosevelt's faux pas was Jimmy Carter's younger brother Billy, who gained celebrity for his boozy, good-ol' boy likability. In the late 1970s, he endorsed a product called Billy Beer. The cans read: "Brewed expressly for and with the personal approval of one of America's all-time Great Beer Drinkers – Billy Carter."

Even though Trump's lawyers insist she has no plan to profit from her time as first lady, Norm Eisen, a former Obama administration ethics lawyer, said that at some level, the language in her lawsuit has to be taken at face value.

"You're not allowed to make assertions that are not true in legal documents," he said.

Taken literally, Eisen sees the mere idea of creating Melania Inc. as an extension of the criticism that has dogged the president – that his massive business empire is illegally benefiting from Trump's Oval Office perch. "The Trumps are using the White House like the Kardashians used reality TV, to build and vastly expand their business enterprises," he said, with questions being raised about Washington's Trump International hotel courting foreign diplomats for bookings, international deals pursued by the president's sons, Trump's public excoriation of Nordstrom for dropping his daughter's clothing line and continued murkiness about his intent to separate from his business while in office.

There is one thing that current and former first ladies can sell, though, without running into legal or ethical trouble – books.

First lady memoirs are practically their own industry – reliably lucrative products, netting advances of a million dollars and up. Nancy Reagan's "My Turn" and Barbara Bush's "Memoir" reportedly earned $2 million a piece. Laura Bush's "Spoken From the Heart" fetched her a reported $1.6 million advance, and Hillary Clinton was paid $8 million for "Living History." Obama could earn far more than that, according to publishing experts.

So if Melania Trump wants to sell something, perhaps she should start writing.