(CNN) Sen. Cory Booker announced Monday that he will end his campaign after failing to qualify for the Democratic debate planned for Tuesday in Iowa .

"It was a difficult decision to make, but I got in this race to win, and I've always said I wouldn't continue if there was no longer a path to victory," Booker said in an email to supporters Monday.

The New Jersey Democrat's announcement came a day before six presidential candidates will participate in the CNN/Des Moines Register's debate in Des Moines , Iowa. He did not qualify for the event. It also came as the Senate gears up for the impeachment trial of President Donald Trump.

"Our campaign has reached the point where we need more money to scale up and continue building a campaign that can win -- money we don't have, and money that is harder to raise because I won't be on the next debate stage and because the urgent business of impeachment will rightly be keeping me in Washington," Booker wrote.

His announcement marks another departure of a high-profile black candidate from the 2020 race. After not making the December debate, Booker criticized the rules that kept him from qualifying for the event and was outspoken about the growing lack of diversity on stage.

Booker made the decision over the weekend to drop out of the race, a campaign aide tells CNN.

The looming impeachment trial, which would have kept Booker off of the trail for some time, was "a piece, but not a big piece" of his decision. Most importantly, Booker believed he did not have the resources to truly be competitive moving forward. Booker reported raising $6.6 million in the last quarter of 2019, a fraction of the amounts raised by the top Democratic candidates. It's not clear how much money he had left in the bank.

It is also not clear whether Booker plans to endorse another Democratic candidate in the primary, the aide said, but as his statement made clear, he will support the nominee.

The New Jersey Democrat ran for president aiming to restore a sense of community and mend the moral fabric of America.

Booker launched his candidacy in February 2019 with a message he would remain faithful to throughout his campaign, calling on Americans who are feeling "a common pain" to come together in "common purpose" for greater justice and systemic change.

Booker pressed for reforming the nation's gun laws, including establishing a national gun license program. He advocated expansive criminal justice reform, including legalizing marijuana and expunging records of those already convicted for marijuana-related crimes. And Booker frequently shone a light on policy blindspots concerning marginalized communities, citing his own low-income, minority-majority neighborhood in Newark.

But unlike some of his rivals, Booker focused less on policy than on the "spiritual" side of the presidency. He viewed the White House as a moral post from which to inspire and guide a dispirited nation.

Even as his campaign failed to pick up steam, Booker rejected pivoting from that message or overhauling his strategy. Instead, he continued to preach the need for "radical love" -- resisting the political incentive structure, in the age of Trump, that rewards channeling the anger of some Democratic activists.

Photos: Former presidential candidate Cory Booker Photos: Former presidential candidate Cory Booker US Sen. Cory Booker greets the audience at a Conference of Mayors meeting in January 2019. Hide Caption 1 of 41 Photos: Former presidential candidate Cory Booker Booker's parents, Cary and Carolyn, were among the earliest black executives at IBM. The family grew up in the affluent community of Harrington Park, New Jersey. Cory is third from left. His younger brother, Cary, is with his dad at left. Hide Caption 2 of 41 Photos: Former presidential candidate Cory Booker Booker played football at Stanford University. He also served as student body president and ran a crisis hotline for students. After getting his master's degree, he would go on to attend Oxford University as a Rhodes Scholar. He graduated from Yale Law School in 1997. Hide Caption 3 of 41 Photos: Former presidential candidate Cory Booker Booker, second from left, poses with his parents and his brother after he was elected to the Municipal Council of Newark in 1998. It was his first public office. Hide Caption 4 of 41 Photos: Former presidential candidate Cory Booker Booker concedes defeat after losing the 2002 mayoral race to incumbent Sharpe James. But he would be back four years later. Hide Caption 5 of 41 Photos: Former presidential candidate Cory Booker Booker celebrates in May 2006 after he was elected as Newark's mayor. He defeated Deputy Mayor Ronald Rice after incumbent Sharpe James decided to focus on the state Senate. Hide Caption 6 of 41 Photos: Former presidential candidate Cory Booker Booker takes the oath of office in July 2006. Next to him, holding the Bible, is his mother, Carolyn. Also holding the Bible in the foreground is Booker's grandmother, Adeline Jordan. Hide Caption 7 of 41 Photos: Former presidential candidate Cory Booker Booker walks on the newly refurbished City Hall dome in Newark in November 2006. Hide Caption 8 of 41 Photos: Former presidential candidate Cory Booker From left, Booker, Lt. Gov. candidate Loretta Weinberg, US President Barack Obama and New Jersey Gov. Jon Corzine wave at a gubernatorial campaign rally in November 2009. Hide Caption 9 of 41 Photos: Former presidential candidate Cory Booker Booker helps cut the ribbon at the opening of affordable housing in Newark that was funded through Jon Bon Jovi's JBJ Soul Foundation in December 2009. Hide Caption 10 of 41 Photos: Former presidential candidate Cory Booker Booker stands behind Facebook CEO Mark Zuckerberg, who donated $100 million to help improve public schools in Newark. His donation was the first grant handed out by his new foundation, Startup: Education. The foundation is focused on bettering education in the United States. Hide Caption 11 of 41 Photos: Former presidential candidate Cory Booker Booker shovels snow to help dig out people's vehicles in Newark in January 2011. While serving as mayor, Booker developed a reputation for engaging in personal acts of heroism such as rescuing a neighbor from a house fire and chasing down a suspected bank robber. Using social media to connect with constituents, he shoveled snowbound driveways by request and invited nearby city residents to his home when Hurricane Sandy caused widespread power outages. Hide Caption 12 of 41 Photos: Former presidential candidate Cory Booker Booker leaps from the wheel cover of a mobile billboard after taking photos on it in February 2011. The truck was driven across the nation to draw attention to US gun laws. Hide Caption 13 of 41 Photos: Former presidential candidate Cory Booker Booker plays a game of one-on-one with pro basketball player Cappie Pondexter in May 2011. Hide Caption 14 of 41 Photos: Former presidential candidate Cory Booker Booker speaks at the Democratic National Convention in September 2012. Hide Caption 15 of 41 Photos: Former presidential candidate Cory Booker Women pose next to Booker's campaign bus during a rally in Newark in August 2013. Booker was running for the US Senate seat that was vacated when five-term incumbent Frank Lautenberg died at the age of 89. Hide Caption 16 of 41 Photos: Former presidential candidate Cory Booker Booker addresses supporters after winning the Democratic primary in August 2013. He went on to defeat Republican Steve Lonegan in October. Hide Caption 17 of 41 Photos: Former presidential candidate Cory Booker Booker takes the oath of office from Vice President Joe Biden during a ceremonial swearing-in at the US Capitol. Hide Caption 18 of 41 Photos: Former presidential candidate Cory Booker Booker confers with US Sen. Kirsten Gillibrand during a Senate subcommittee hearing in November 2013. The hearing, about Hurricane Sandy recovery efforts, was Booker's first since being sworn in. Hide Caption 19 of 41 Photos: Former presidential candidate Cory Booker Booker addresses a gathering of students and parents at his childhood school in Harrington Park, New Jersey, in November 2014. He had just been re-elected a day earlier. Hide Caption 20 of 41 Photos: Former presidential candidate Cory Booker Booker testifies before the Senate Judiciary Committee's Constitution, Civil Rights and Human Rights Subcommittee in December 2014. Hide Caption 21 of 41 Photos: Former presidential candidate Cory Booker Vice President Joe Biden administers the Senate oath to Booker in January 2015. Holding the Bible is Booker's niece, Zelah, and his sister-in-law, Lucille. Hide Caption 22 of 41 Photos: Former presidential candidate Cory Booker Booker talks with US Sen. Chuck Schumer after a news conference about Iran in October 2015. Hide Caption 23 of 41 Photos: Former presidential candidate Cory Booker Booker meets with eighth-graders during their end-of-year trip to Washington in May 2016. Hide Caption 24 of 41 Photos: Former presidential candidate Cory Booker Booker campaigns with Democratic presidential candidate Hillary Clinton at a cafe in Newark in June 2016. Hide Caption 25 of 41 Photos: Former presidential candidate Cory Booker During a news conference in June 2016, Booker embraces the Rev. Sharon Risher, a clinical trauma chaplain who lost her mother and two cousins in a church shooting in Charleston, South Carolina. Democratic senators were calling for gun-control legislation after a mass shooting at an Orlando nightclub. Hide Caption 26 of 41 Photos: Former presidential candidate Cory Booker Booker speaks at the Democratic National Convention in July 2016. Hide Caption 27 of 41 Photos: Former presidential candidate Cory Booker Booker speaks to members of the media following a confirmation hearing for US Sen. Jeff Sessions, a Republican from Alabama who was nominated to be attorney general. Booker broke with tradition and became the first sitting senator to testify against a fellow senator's nomination for a Cabinet post. Hide Caption 28 of 41 Photos: Former presidential candidate Cory Booker Booker looks on as Scott Pruitt, Oklahoma's attorney general and Donald Trump's pick to run the Environmental Protection Agency, testifies at his confirmation hearing in January 2017. Hide Caption 29 of 41 Photos: Former presidential candidate Cory Booker Booker and US Sen. Elizabeth Warren talk before the start of a July 2017 news conference that introduced the Dignity for Incarcerated Women Act. Hide Caption 30 of 41 Photos: Former presidential candidate Cory Booker Booker boards an elevator at the Capitol in January 2018. Hide Caption 31 of 41 Photos: Former presidential candidate Cory Booker Booker questions Judge Brett Kavanaugh, President Trump's nominee for the US Supreme Court, during Kavanaugh's confirmation hearing in September 2018. Hide Caption 32 of 41 Photos: Former presidential candidate Cory Booker Booker poses for a photo with a group of visitors at the Hart Senate Office Building in Washington in January 2019. Hide Caption 33 of 41 Photos: Former presidential candidate Cory Booker Booker joins actors Taylor Trensch and Rosario Dawson backstage at the hit Broadway musical "Dear Evan Hansen" in January 2019. Dawson confirmed in March that she and Booker were dating. Hide Caption 34 of 41 Photos: Former presidential candidate Cory Booker Booker walks with NAACP leaders during a Martin Luther King Jr. Day march in Columbia, South Carolina, in January 2019. Hide Caption 35 of 41 Photos: Former presidential candidate Cory Booker After announcing that he would be running for president, Booker speaks to the press outside his home in Newark in February 2019. Hide Caption 36 of 41 Photos: Former presidential candidate Cory Booker Booker speaks during a campaign event in Des Moines, Iowa, in February 2019. Hide Caption 37 of 41 Photos: Former presidential candidate Cory Booker Someone takes a photo of Booker during a campaign stop in Claremont, New Hampshire, in March 2019. Hide Caption 38 of 41 Photos: Former presidential candidate Cory Booker Booker looks to be called on during the CNN Democratic debates in July 2019. Hide Caption 39 of 41 Photos: Former presidential candidate Cory Booker Booker explores the Iowa State Fair in August 2019. Hide Caption 40 of 41 Photos: Former presidential candidate Cory Booker Booker is seen after a Democratic debate in Westerville, Ohio, in October 2019. Hide Caption 41 of 41

At times, Booker's stump speech could assume the quality of a TED Talk or a sermon, moving members of the audience to tears and converting many to supporters. But ultimately that small-scale passion did not translate into broader support for Booker, who polled in the low single digits for much of his campaign.

His advisers maintained that if only Booker could introduce himself to more voters, he stood a chance of becoming more competitive. But a few factors prevented the sort of breakout moment that many political prognosticators believed would come for Booker, but never did.

Throughout 2019, Booker's fundraising paled in comparison to that of the top-tier Democratic candidates, limiting his capacity to expand his campaign team and advertise on television. In December, Booker failed to qualify for the debate stage, in part because his campaign did not have enough money to boost his polling.

Booker could also be difficult to define as a candidate. Although he aimed for a middle-road between the party's most progressive candidates and its moderate entrants, Booker might have landed in a political no-man's-land, without a clear ideological brand to attract undecided voters.

Booker's background as a former mayor and Rhodes Scholar did not receive the same attention as those of others, like Pete Buttigieg, another Rhodes Scholar and now-former mayor of South Bend, Indiana, who became an object of the public's and media's fascination.

Booker also was not eager to highlight contrasts with his rivals, even as other candidates benefited from such attacks.

One exception was when Booker, over the summer, took on former Vice President Joe Biden for using the term "boy" in a manner demeaning to African Americans. When Biden suggested Booker should be the one to apologize, Booker did not back down.

"I was raised to speak truth to power and that I shall never apologize for doing that," Booker told CNN's Don Lemon at the time. "And Vice President Biden shouldn't need this lesson."

Booker was consistently lauded for his debate performances, when he often commanded the stage. But those were ultimately not enough to boost his profile in the crowded 2020 primary.

When Booker failed to meet the polling requirements for the December Democratic debate, he acknowledged it was a setback for his campaign, but vowed to keep pushing on, citing his strong organization in Iowa and other early states.

But his path to an upset was further complicated by the looming impeachment trial in the Senate, which would have pulled him off the campaign trail.

In his announcement to supporters, Booker said he would do "everything in my power to elect the eventual Democratic nominee for president, whomever that may be, and to elect great Democrats to the Senate and up and down the ballot."