Warren reveals why she didn't run for president in 2016

Massachusetts Senator Elizabeth WarrenElizabeth WarrenDem senators ask Bannon for more info about Breitbart contact Senate Dems want Trump to release ethics waivers, visitor logs Warren congratulates Scott Brown on ambassador nomination MORE reveals why she decided against running for president in 2016 in a new book to be released Tuesday.

In "This Fight Is Our Fight," the progressive favorite recalls asking her husband, Bruce Mann, for his thoughts on a 2016 run for the White House. 

While her husband was supportive, he was wary that a presidential run would be more intense than her 2012 Senate race against then-incumbent Sen. Scott Brown. 

"The Senate thing was bad enough, and running for president would be worse — a lot worse,” he had warned her.

During the 2012 Senate campaign, Brown often referred to Warren as "Professor Warren," a shot at her Harvard credentials, and targeted her for claiming Native American ancestry during her hiring process. Despite the attacks, Warren won the election by 8 points. 

Warren was floated by the more liberal wing of the Democratic Party as an alternative to Hillary ClintonHillary Rodham ClintonThe Hill's 12:30 Report Mark Cuban gives Trump presidency a "C-" Georgia should still be on the mind of Democrats MORE last year. In the end, Warren declined to run, opening the door for Vermont Sen. Bernie SandersBernie SandersEx-aide: Obama still the leader of the Democratic Party Sanders endorses Ossoff, but won't call him a progressive The Hill's 12:30 Report MORE to challenge Clinton for the Democratic nomination.

Many political observers now see Warren as a likely presidential candidate in 2020, when Democrats will be looking for a new standard-bearer to take on President Trump.

Despite Warren's refusal to run in 2016, she remained a target for Republicans during the election. During rallies, then-candidate Trump referred to her as "Pocahontas" as a way to make fun of her claiming Cherokee heritage. 

In her book, Warren talks about how the Clinton and Sanders campaigns both pressured her for an endorsement. 

"I didn’t want to undermine either of our candidates or to short-circuit any part of that debate,” Warren writes.