Sen. Kamala Harris has suspended her presidential bid, bringing to a close her historic effort to secure the Democratic nomination.

"I’ve taken stock and looked at this from every angle, and over the last few days have come to one of the hardest decisions of my life. My campaign for president simply doesn’t have the financial resources we need to continue," the California lawmaker wrote in a letter to supporters. "I’m not a billionaire. I can’t fund my own campaign. And as the campaign has gone on, it’s become harder and harder to raise the money we need to compete. In good faith, I can’t tell you, my supporters and volunteers, that I have a path forward if I don’t believe I do. So, to you my supporters, it is with deep regret -- but also with deep gratitude -- that I am suspending my campaign today."

Harris took a hard look at the campaign’s resources over the Thanksgiving holiday and made the decision Monday after discussing the path forward with her family and senior aides, a senior Harris aide told ABC News. She will travel to the early states this week to personally and privately thank staff and supporters there for their hard work and dedication to the campaign, the aide added.

Harris' announcement comes after her campaign drastically cut her staff in October, funneling most of her campaign’s resources toward working on a strong victory in Iowa and leaving other early voting states such as New Hampshire and South Carolina with minimal staffing and funding.

“I’m moving to Iowa,” the senator joked at rallies, as she vowed to campaign in the state each week.

Still she plateaued in the polls in the single digits. In a recent ABC News and Washington Post poll, Harris only garnered 2% support among Democrats and Democratic-leaning Independents.

Harris entered the race in January speaking before a crowd of 20,000 people, one of the largest in the 2020 cycle. The senator’s presidential hopes were amplified by a sudden boost of support after a breakthrough moment during the first Democratic presidential debate. On the debate stage, Harris, who is black and Indian American, challenged former Vice President Joe Biden on his past stances on busing policies.

"There was a little girl in California who was part of the second class to integrate her public schools and she was bused to school every day. That little girl was me," Harris said.

On Tuesday, Biden complimented Harris as a competitor.

"She is a first rate intellect, a first rate candidate and a real competitor," he told reporters at an event in Iowa. "I have mixed emotions about it because she is really a solid, solid person and loaded with talent. I’m sure she’s not dropping out on wanting to make the changes she cares about.”

Those changes, Harris underscored on the trail and in her letter to supporters, centered on "fighting for people whose voices have not been heard or too often ignored."

On the campaign trail, Harris’ record as district attorney of San Francisco and later attorney general of California, became a frequent area of criticism from her fellow presidential contenders.

As a presidential candidate, Harris' team sought to highlight her efforts as a progressive prosecutor who championed criminal justice reform and held the powerful accountable. In stump speeches across the country, Harris made a pitch to voters about why she was best poised to “prosecute the case against four more years of Donald Trump.”

Harris' popularity rose in part because of her harsh questioning of Trump cabinet nominees such as Supreme Court Justice Brett Kavanaugh. It was those same skills her team tried to highlight as the House impeachment inquiry into President Trump got underway.

President Donald Trump weighed in on Harris' campaign suspension with a short tweeted response: "Too bad. We will miss you Kamala!"

Earlier in the day, the Trump campaign and some of its staffers mocked Harris on social media over dropping out of the Democratic primary on Tuesday —including congratulating Rep. Tulsi Gabbard, D-Hawaii, a candidate with whom the California senator had differed on the debate stage.

"Somehow we will press on," Trump campaign communications director Tim Murtaugh told ABC News when asked about Harris suspending her campaign.

Harris responded to Trump on Twitter on Tuesday night with a promise: "Don’t worry, Mr. President. I’ll see you at your trial."

For her part, Gabbard wished Harris well tweeting "Sending my best wishes to @KamalaHarris, her family & supporters who have campaigned so hard. While we disagree on some issues, we agree on others & I respect her sincere desire to serve the American people. I look forward to working together on the challenges we face as a nation."

Others, such as former Democratic presidential nominee and Housing and Urban Development Secretary Julian Castro also lauded Harris for her efforts.

"I’m so thankful for @KamalaHarris’s friendship and candidacy in this race. As a child of immigrants, she’s been a lifelong fighter for opportunity and justice for all Americans, and I’m glad she’ll keep fighting for an America where everyone counts," he tweeted.

Former Democratic presidential nominee and Secretary of State Hillary Clinton sought to offer words of encouragement to those who volunteer for candidates who end bids.

"To all the candidates, staff, and volunteers who have worked their hearts out for presidential campaigns that have ended—remember that fighting for what you believe in is always worth it," she tweeted.

ABC News' MaryAlice Parks and Will Steakin contributed to this report.