Hillary Clinton has ruled out a third US presidential run in 2020.
"I'm not running, but I'm going to keep on working and speaking and standing up for what I believe," Mrs Clinton told New York's News 12 TV channel.
As the Democratic candidate in 2016, Mrs Clinton was widely expected to become the first female US president, before a shock defeat by Mr Trump.
Asked by News 12 if she would run again for any public office in future, she said: "I don't think so."
Meanwhile, former New York Mayor Michael Bloomberg ruled himself out of the 2020 race.
"I believe I would defeat Donald Trump in a general election," the billionaire said in a statement on Tuesday afternoon. "But I am clear-eyed about the difficulty of winning the Democratic nomination in such a crowded field."
While there would be no higher honor than serving as president, my highest obligation as a citizen is to help the country the best way I can, right now. That's what I'll do, including the launch of a new effort called Beyond Carbon. My full statement: https://t.co/b3cQUF1PhU— Mike Bloomberg (@MikeBloomberg) March 5, 2019
Mrs Clinton's interview was the first time she definitively rebutted speculation that she might take on Mr Trump again in 2020.
She said she had spoken to some of the declared 2020 Democratic candidates. "I've told every one of them, don't take anything for granted," she said.
Mrs Clinton was the first female presidential nominee for a major US party in the nation's history. Her ascension to the top office was widely seen as all but guaranteed, but she was dogged by accusations of being overly reliant on wealthy donors, too close to Wall Street and out of touch with younger voters.
She was relentlessly pilloried by Mr Trump, who goaded crowds on the campaign trail to chant "Lock her up".
Her defeat prompted a period of soul-searching for the Democratic Party, which is now gearing up for a wide-open primary contest that has already seen more than 10 contenders announce a run.
Reacting to Mrs Clinton's decision to stay out of the race, Mr Trump tweeted to say sarcastically that she would "be sorely missed".
“(Crooked) Hillary Clinton confirms she will not run in 2020, rules out a third bid for White House.” Aw-shucks, does that mean I won’t get to run against her again? She will be sorely missed!— Donald J. Trump (@realDonaldTrump) March 5, 2019
Mrs Clinton responded by tweeting a clip from the 2004 teen comedy Mean Girls in which a character asks: "Why are you so obsessed with me?"
Democratic trailblazer shuts the door
The late Senator Ted Kennedy, who unsuccessfully sought the Democratic nomination in 1980, used to quip that he didn't think about running for president anymore … but he didn't think about it any less.
Hillary Clinton came ever-so-close to the prize in 2016 and clearly still harbours White House dreams. The reality, however, is a failed nominee hasn't made a second run since Richard Nixon in the 1960s.
Every month or so for the past two years there's been a spate of "she might run" speculation - some fuelled by her former staff, some perhaps the product of conservatives looking to rile up their base. There still isn't anyone on the Democratic side who provokes the right quite like the former first lady.
Despite this speculation, Mrs Clinton never took decisive steps toward another campaign - and now she has publicly closed the door.
She'll have to be satisfied with going down in history as the first woman to win a major party's presidential nomination. And while she never did break that final glass ceiling, with six woman Democrats already in the 2020 race, she might also be viewed as a trailblazer, who paved the way for others to follow.
Who is running in 2020?
Vermont senator and 2016 Democrat primary runner-up Bernie Sanders is the latest to throw his hat in the ring for the Democrats. Mr Sanders' name recognition and base of support among the party's left has catapulted him towards the front of the pack.
He joins Massachusetts Senator Elizabeth Warren, who was the first big name to declare a run, as well as New Jersey Senator Cory Booker and California Senator Kamala Harris.
Also in the running are New York Senator Kirsten Gillibrand; Minnesota Senator Amy Klobuchar; the Mayor of San Antonio, Texas, Julian Castro; and the Mayor of South Bend, Indiana, Pete Buttigieg, who is the first openly gay person to run for president.
Some of the most talked-about names are yet to declare their intentions. The former Vice-President, Joe Biden, is considering a run. He enjoys the best name recognition in the country, and some analysts say he would be an early front-runner if he were to enter the race.
Beto O'Rourke, a former congressman from Texas who drew national attention when he ran an unexpectedly close Senate race against Republican incumbent Ted Cruz, has kept fans and potential donors waiting as he weighs his options.
Mr O'Rourke ran an unconventional campaign for the Senate, posting unvarnished social media updates as he drove through all 254 counties in the state, fuelled by millions in small-dollar donations.
Who will take on Trump in 2020?
Who is vying for the Democratic nomination?