Kate Andersen Brower is the author of the best-sellers "First Women: The Grace and Power of America's Modern First Ladies" and "The Residence: Inside the Private World of the White House." Unless otherwise noted, facts in this piece reflect research from those works. The opinions expressed here are hers.

(CNN) When former Vice President Al Gore emerged from his meeting with President-elect Donald Trump, he made sure to tell reporters that he met with Ivanka Trump first but spent "the bulk of the time" with her father.

Gore, an outspoken advocate for fighting climate change, was obviously there seeking to find whatever common ground he could with the new administration, led by someone whose positions on climate change are at best, unpredictable

The fact that Gore did this by first meeting with Trump's daughter is remarkable, especially amid reports that Ivanka and her husband, Jared Kushner, are considering uprooting their family from New York to Washington while incoming first lady Melania Trump stays put in her Trump Tower penthouse. It begs the question: Who exactly is going to be the first lady come noon January 20? The answer, I think, is no one. Melania may prefer, it seems, to remain in New York with son Barron, but that doesn't make Ivanka the de facto first lady. It makes her someone potentially much more publicly powerful.

Ivanka is more than a first daughter and more than a first lady: She is her father's most effective public defender and she humanizes him in a way Melania cannot. Melania's decision to stay in New York while her son finishes the school year does leave a vacuum for the position of first lady, but Ivanka will be far too busy to be her father's helpmate. She'll be meeting with high-profile Democrats like Leonardo DiCaprio, with whom she reportedly has already met, who see her as their lifeline to her father's administration. The Trumps' social secretary will have to take the lead and have final say on guest lists and china patterns.

This isn't the first sign that Ivanka's influence on her father outpaces that of her stepmother. After Melania was criticized for cribbing parts of her remarks at the Republican National Convention from first lady Michelle Obama, Ivanka positioned herself as the moderate in her father's circle during her own speech at the convention, in which she spoke out strongly for progressive values like child care tax credits.

Melania was conspicuously absent when her husband announced Mike Pence as his running mate, marking the first time in modern campaign history that the wife of a presidential candidate was not there for the public announcement. Of course Ivanka and Jared stood gamely by Trump's side.

Traditionally, most children of presidential candidates have shown a general reluctance to engage in the blood sport of politics. Before George W. Bush decided to run for president in 2000, Jenna Bush pleaded with her father, "Oh, I just wish you wouldn't run. It's going to change our life."

There have been some first daughters who have played a role in their fathers' administrations, usually as White House hostess when their mothers were unavailable. Martha Jefferson Randolph, whose mother died almost 20 years before Thomas Jefferson was inaugurated, did so, as did Margaret Truman, whose mother, Bess, often left Washington for the calm of her home in Independence, Missouri.

In the latter half of the 20th century, there were a slew of young adult children living in the White House. These presidential offspring offered advice but they were largely confined to the campaign and were not considered top White House advisers.

Luci Johnson, LBJ's youngest daughter, said her father would grade the campaign speeches she made on his behalf. President Gerald Ford's son, Steve, was 18 years old when his father pardoned President Nixon, a month after Nixon announced his resignation. Steve advised against it and told his father: "They're going to crush you if you pardon Nixon." The Reagans' son, Ron, remembers getting into a heated debate about the Iran-Contra affair with his parents in the White House residence.

But there has never been a first daughter who was also a serious political adviser -- and certainly not like this, where the lines of business interest, of politics, and of diplomacy are so thoroughly blurred between family and the West Wing.

Trump is also the oldest elected president in American history. At 70 he is a year older than Ronald Reagan was when he was sworn in. Trump named three of his children, all in their thirties, to his transition team, and the age of his children poses ethical questions that have largely been irrelevant for more than 20 years because of the relatively young presidents who have occupied the White House.

(The Clintons came to Washington with 12-year-old Chelsea, Jenna and Barbara Bush were both college students during the beginning of their father's presidency, and Sasha and Malia Obama were 7 and 10 years old when they moved into the White House.)

We rarely hear the voices of the children living in the White House because they have been so young and because they have largely been considered off-limits to the press.

Perhaps the most famous exception prior to Ivanka was Alice Roosevelt Longworth, President Theodore Roosevelt's first daughter, who was an endless source of fascination for the press. Alice smoked in public, wore pants and engaged in other "unladylike" behavior just after the turn of the 20th century.

Dubbed "Princess Alice," she did not shy away from controversy. Alice admitted rather coldly that she felt "ecstatic" when President William McKinley was assassinated and her father became the 26th president. It is hard to imagine the always composed Ivanka saying something so unguarded in public. "I just want to be a good daughter," Ivanka insists, even when it's clear she wants to do much more than that.

And no presidential daughter has come to her father's defense quite like Ivanka has since Julie Nixon Eisenhower. Julie is the only daughter of a president who has been so publicly devoted. As the Watergate investigation dragged on, Julie stood by her father's side. In a diary entry less than a year before her father's resignation, Julie wrote: "Fight, fight, fight."

She took the bold step of standing in her father's place during a news conference at the height of the scandal. "I have seen what my father has gone through, and I am so proud of him that I would never be afraid to come out here. ... I am not trying to answer questions for him. I am just trying to pray for enough courage to meet his courage."

Julie's praise for her father is not unlike what we've heard from Ivanka, who defended Trump from charges of misogyny and insisted : "My father is a feminist. He's a big reason I am the woman I am today." That devotion is returned: During the campaign, when asked to name a woman he would consider appointing to his Cabinet, Trump mentioned Ivanka. "She's very popular, she's done very well."

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In a 1970 memo, top Nixon aide H.R. Haldeman described the need to find full-time jobs for Julie and her sister Tricia, then both in their early twenties. "Income is not a factor -- the President will pay them himself." In the memo Haldeman acknowledged that Nixon's daughters could not "work for the government, or for the Nixon Foundation." Even Nixon recognized the limits of his own power and the influence his daughters should have in his White House.

There are many lessons Trump could take from Richard Nixon's behavior about what not to do as president -- flouting nepotism in the Oval Office is only one among many.