New Jersey Senator Cory Booker suspended his presidential bid on Monday, acknowledging what has been apparent for months — that he isn't building the support needed to win the Democratic nomination.

Booker, who will be participating in the Senate impeachment trial of President Trump, wrote in a Medium post published Monday morning that the best way to beat Mr. Trump at the ballot box in 2020 is "to reignite our spirit of common purpose to take on our biggest challenges and build a more just and fair country for everyone."

"I will carry this fight forward — I just won't be doing it as a candidate for president this year," Booker wrote. "It's with a full heart that I share this news — I've made the decision to suspend my campaign for president."

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Just last week, he had told the Associated Press that his campaign's internal metrics indicated he'd finish in a "pretty exciting place" in the Iowa caucuses, though he said that a Senate trial that lasted just two weeks would force him to cancel "literally dozens of events" in Iowa.

Booker launched his campaign last February and despite building a formidable ground operation in the early states, he could never break into the top tier, polling consistently in the single digits. Booker registered 3% support in a Des Moines Register poll published Friday.

The former Newark mayor consistently lagged behind his competitors in fundraising, a point that Booker alluded to in his post. Booker also mentioned the looming Senate impeachment trial, which will make it difficult for him to campaign while the trial is underway.

"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.

After failing to meet the debate stage in December, Booker made a direct plea to the Democratic Party to change the thresholds to qualify for debates. With California Senator Kamala Harris suspending her campaign earlier that month, there were no African-Americans on stage at the debate.

Booker also did not qualify for this Tuesday's debate in Iowa, which will be the first to feature only white candidates.

"Of all of the people who've qualified for the next Democratic debate stage, not one is a person of color," Booker wrote in an email to supporters a couple of days ago. "For a party as diverse as ours, in an election where communities of color will decide the outcome, that's wrong."

Booker, whose message primarily focused on unification and resurrecting former President Obama's winning coalition, also criticized the late entrance of former New York City Mayor Michael Bloomberg to the presidential race.

"It is a problem that we now have an overall campaign for the 2020 presidency that has more billionaires in it than black people," Booker said after Bloomberg entered the race.

Booker has been one of the leading voices on gun violence prevention and criminal justice reform in the presidential race. In May, Booker released his gun safety plan, which called for a gun licensing program. And on the campaign trail, Booker often touted his work in passing criminal justice reform under the Trump administration.

Booker's withdrawal from the race comes just weeks away from his campaign's one-year anniversary. He originally announced he was running for president on February 1, 2019.