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

Massachusetts Senator Elizabeth WarrenElizabeth Ann WarrenTim Ryan doesn't back impeachment proceedings against Trump Schiff: Democrats 'may' take up impeachment proceedings Trump claims Democrats' plans to probe admin will cost them 'big time' in 2020 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 Diane Rodham ClintonThorny part of obstruction of justice is proving intent, that's a job for Congress Nadler: I don't understand why Mueller didn't charge Donald Trump Jr., others in Trump Tower meeting Kellyanne Conway: Mueller didn't need to use the word 'exoneration' in report MORE last year. In the end, Warren declined to run, opening the door for Vermont Sen. Bernie SandersBernard (Bernie) SandersCory Booker has a problem in 2020: Kamala Harris Wage growth shaping up as key 2020 factor for Trump Booker to supporter who wanted him to punch Trump: 'Black guys like us, we don't get away with that' 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.