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WASHINGTON — Then-Democratic National Committee head Donna Brazile considered replacing Hillary Clinton at the top of the party's ticket last year after the presidential nominee appeared unsteady and stumbled following a September 11 memorial service in New York, Brazile writes in her new book.

Brazile, a longtime Clinton friend and ally, was stunned by what happened after the Ground Zero event and the "shameful" fact that she and everyone else had been kept in the dark about the candidate's health.

Only hours after Clinton was spotted unsteady and requiring support to get into her van as she left the service did the campaign reveal that the candidate had been suffering from pneumonia and had become dehydrated on the unseasonably warm day.

Former Democratic presidential nominee Hillary Clinton leaves the 9/11 Commemoration Ceremony at the National September 11 Memorial & Museum on Sept. 11, 2016, in New York City. Justin Sullivan / Getty Images file

As rumors swirled about Clinton's health and the future of her presidential campaign, representatives of Vice President Joe Biden, Sen. Bernie Sanders, I-Vt., and former Maryland Gov. Martin O’Malley contacted Brazile, she writes, apparently to offer their services.

"Gee, I wonder what he wanted to talk to me about?" Brazile writes about Biden.

Former Clinton campaign officials said in an open letter Saturday they were “shocked” by the news that Brazile considered a replacement.

"It is particularly troubling and puzzling that she would seemingly buy into false Russian-fueled propaganda, spread by both the Russians and our opponent, about our candidate's health," the former campaign officials said in the letter.

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The Washington Post first reported the news of the book, titled "Hacks: The Inside Story of the Break-ins and Breakdowns That Put Donald Trump in the White House."

NBC obtained a copy of the book subject to a confidentiality agreement with the publisher and can confirm the information that the Washington Post has published is accurate. NBC is honoring its agreement with the publisher and is not publishing additional details from the book.

Brazile writes that she considered several potential replacements for Clinton and Sen. Tim Kaine, D-Va., the vice presidential nominee, and concluded Biden and Sen. Cory Booker, D-N.J., would be the strongest combination to beat Donald Trump in November.

Brazile, who was abruptly brought on to replace former DNC chairwoman Debbie Wasserman Schultz during the party’s convention last summer, did not have the power to unilaterally remove Clinton and Kaine.

But DNC rules give the party's chairman the authority to set the ball in motion.

"In the event of death, resignation or disability of a nominee of the Party for President or Vice President after the adjournment of the National Convention, the National Chairperson of the Democratic National Committee shall confer with the Democratic leadership of the United States Congress and the Democratic Governors Association and shall report to the Democratic National Committee, which is authorized to fill the vacancy or vacancies," the party's Convention Call states.

Furthermore, the DNC bylaws state the chair is the one to call "a special meeting to fill a vacancy on the National ticket."

However, after several hours of serious contemplation, Brazile writes that she could not drag the party through such an ugly process, and that even public consideration of replacing Clinton was unacceptable.

"I thought of Hillary, and all the women in the country who were so proud of and excited about her. I could not do this to them," Brazile writes.

Still, the incident underscores Brazile's disillusionment with the Clinton campaign — a stunning and explosive break for a veteran of the party’s establishment who had been a superdelegate for Clinton.

The former Clinton campaign officials said in the letter Saturday: “We were shocked to learn the news that Donna Brazile actively considered overturning the will of the Democratic voters by attempting to replace Hillary Clinton and Tim Kaine as the Democratic Presidential and Vice Presidential nominees.”

The signers of the letter include campaign chairman John Podesta, communications director Jennifer Palmieri and strategist Joel Benenson.

The letter from Clinton campaign officials said Brazile "came in to take over the DNC at a very difficult time," that she is a longtime friend of many of the officials and they were grateful for her taking over the DNC.

"But we do not recognize the campaign she portrays in the book,” The Clinton campaign officials said in the letter.

Brazile also excoriates former President Barack Obama for neglecting the party under the leadership of Wasserman Schultz, whom Brazile seems to hold in an even lower regard.

The book is due out Tuesday.