By Chris Cillizza, CNN Editor-at-large

(CNN) -- On Tuesday night, word came that Barbara Bush, the 92-year-old doyenne of the first family of Republican politics, had passed away.

To some, Barbara Bush is nothing but a shock of white hair and a vague memory that she was once First Lady of the United States. But, she is much, much more than that -- one of only two women ever to be the wife and mother of presidents, among the most beloved first ladies ever and the unquestioned leader of her prominent political family.

For more context on Barbara Bush and her role in American politics, I reached out to Kate Andersen Brower. Brower, a CNN contributor, wrote "First Women: The Grace and Power of America's Modern First Ladies" and has a new book out June 5 entitled "First in Line: Presidents, Vice Presidents and the Pursuit of Power."

Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: Barbara Bush is the wife and mother to a president -- a unique historical distinction. How does she see herself in that role?

Brower: She is a devoted wife and mother and she is loyal to her husband who she called "a saint." (She has a very dry sense of humor so she would often say things like I have the "perfect family" tongue-in-cheek, but when she calls her husband a z'saint," I think she means it.)

They have been married for 73 years, the longest presidential marriage in history. She is the matriarch of the Bush family but also the matriarch of the Republican Party -- a party she probably doesn't recognize anymore. She represents an era of civility and decorum that is sadly lacking in both political parties today.

Cillizza: She has long been cast as the iron fist of the family. How much of a factor was she in the political career of her husband and oldest son?

Brower: Her family calls her "the enforcer," and when George H.W. Bush was president, he would tell reporters, "Look out, the Silver Fox is really mad at you" if a story they wrote had offended him. In that way, she was like Nancy Reagan minus the negative public perception. Inside the White House, aides and reporters knew not to cross her. She was a hugely popular first lady who was dispatched to New Hampshire to file the papers for Bush when he ran for re-election and she spent more time campaigning in New Hampshire than her husband did. (Editor's note: Barbara Bush actively campaigned for her son, Jeb, during the 2016 New Hampshire primary.) She helped him win his first ever election by campaigning in 189 precincts in Harris County, Texas, in 1962 when he ran his first campaign for Republican Party county chairman. She is his greatest fan and adores him.

Cillizza: Barbara Bush was not initially enthusiastic about Jeb Bush's 2016 campaign. Why not?

Brower: She strongly believed that it was someone else's turn. She was the mother of six children and, as you mentioned, she was one of only two first ladies who was also the mother of a president, a distinction she shared with John Adams' wife Abigail, who was the mother of John Quincy Adams.

The Bushes were in this very tough position of having to watch their sons endure the disappointments that accompany political life. They were surprised when Jeb, who seemed like his father's heir apparent to the presidency, lost his first run for governor in Florida in 1994 and that same year his brother, George W., won the governorship in Texas. George H.W. Bush said at the time, "The joy is in Texas, but our hearts are in Florida."

The stress weighed on Barbara, and one former White House usher who worked at the White House when the Bushes were in office described how difficult it was for them. He watched Barbara and Bush 41 celebrate their son's second inauguration as president in 2005 with most of their large family gathering for brunch in the second-floor family dining room, when she was in the odd position of comforting Jeb, who was governor of Florida at the time and obviously upset about something. Barbara and George H.W. Bush were standing in the hallway outside of the Queens' Bedroom and the Lincoln Bedroom trying to comfort Jeb while George W. Bush was celebrating. Here she was, with one son celebrating a second presidential victory down the hall as she was comforting her other son, who was obviously dejected about something.

Cillizza: She was not shy about her views on Donald Trump, at one point asking publicly how women could vote for him. Did that view of the current president mellow? Or did it harden with time?

Brower: I don't know the answer to this. I know that Nancy Reagan was not happy about Donald Trump co-opting her husband's legacy or any comparisons to Reagan. Barbara Bush was not one for complaining and I think she would have very little sympathy for the current inhabitants of the White House.

She told me "there's something wrong" with any first lady who doesn't understand the incredible opportunity she has. She was the most beloved first lady among the butlers and maids on the residence staff. She told me, "I'd like to go back and live there and not have the responsibility." She enjoyed her life and had fun as first lady -- that's something we don't see anymore. Everything has become so serious and being first lady seems like a chore rather than an honor.

Cillizza: Finish this sentence: The lasting legacy of Barbara Bush on the White House will be ." Now, explain.

Brower: "The lasting legacy of Barbara Bush on the White House will be compassion."

Literacy was her main focus as first lady but I think her legacy will be her ability to empathize with people. She understood the power first ladies have and what she could do with a single image -- in that way she was like Princess Diana.

In 1989, she visited Grandma's House, one of the first homes created to care for infants infected with HIV. She spent nearly an hour there and held babies infected with the HIV virus, which causes AIDS. She wanted to dispel the myth that the disease could be caught simply through physical contact. "You can hug and pick up AIDS babies and people who have the HIV virus" without hurting yourself, she said during the visit. "There is a need for compassion," she said as she cradled a baby.

That one visit was more powerful than any number of speeches or public appearances. She understood that and I think her empathy will be a key part of her legacy.