Democratic presidential candidate Senator Cory Booker (D-NJ) responds to a question during a forum held by gun safety organizations the Giffords group and March For Our Lives in Las Vegas, Nevada, October 2, 2019.

Sen. Cory Booker, D-N.J., dropped out of the 2020 presidential race Monday, after failing to gain traction in national polls and failing to qualify for two Democratic debates.

"Today I'm suspending my campaign for president in the same spirit with which it began," Booker said in a video posted Monday morning.

Booker tweet

"It is my faith in us, my faith in us together as a nation that we share a common pain and common problems that can only be solved with a common purpose and a sense of common cause," he said in the video.

"Campaigning over this last year has been one of the most meaningful experiences of my life. Meeting you, meeting people across this country who believe, who know that we may have challenges right now in our nation, but together, we will rise," Booker said.

Booker launched his bid for the Democratic nomination on Feb. 1, the first day of Black History Month. But the senator from New Jersey failed to gain traction in national polls, reaching under 2% of support, according to RealClearPolitics.

He did not make the stage for the December Democratic debate, criticizing the DNC for upholding hard-to-reach standards to qualify. His departure leaves only three people of color in the race: businessman Andrew Yang, former Massachusetts Gov. Deval Patrick, and Rep. Tulsi Gabbard.

Booker vowed in the video to return to the 2020 campaign trail to support "whoever" becomes the eventual Democratic presidential nominee.

President Donald Trump tweeted about Booker's departure, saying sarcastically that "Booker, who was in zero polling territory, just dropped out of the Democrat Presidential Primary Race. Now I can rest easy tonight. I was sooo concerned that I would someday have to go head to head with him!"

Trump tweet

During his campaign, the former mayor of Newark focused on criminal justice reform and reducing racial and economic inequality. He often referenced living in Newark to highlight his credibility with urban communities. He supported progressive policies such as "Medicare for All" and the Green New Deal to address climate change, but he was considered a moderate.

Ultimately, Booker's message of "love and unity" didn't resonate with voters. Polls consistently put him far behind rivals including former Vice President Joe Biden, Sen. Bernie Sanders, I-Vt., and Sen. Elizabeth Warren, D-Mass.

Biden in a tweet said Booker "campaigned with joy and heart," adding that he "made our politics better just by running."

Biden tweet

In an email immediately after his departure from the race, Booker's campaign said he "ran for president as a uniter and a healer and a uniter and still believes that's what our country needs right now."

Booker's connections with wealthy and influential donors initially appeared to give him a fundraising advantage over the crowded Democratic primary field. But he struggled to gain traction there as well, raising a little more than $6 million in the fourth quarter, badly lagging behind the front-runners.

"We've reached the point where we need more money to scale up and continue building a campaign that can win — money that is harder to raise having been blocked from the next debate stage and with urgent business of impeachment rightly keeping [Booker] in Washington," a Monday email from his campaign said.

But Booker had his moments. When Biden touted his ability as a senator in the 1970s to reach across the aisle to work with segregationists, Booker pounced. He said the comments showed a "terrible lack of understanding" and called on Biden to apologize.

On the debate stage, he criticized Biden's involvement in passing the 1994 crime bill that led to the mass incarceration of African Americans.

"There are people right now in prison for life for drug offenses because you stood up and used that 'tough on crime' phony rhetoric that got a lot of people elected but destroyed communities like mine," Booker said.

— CNBC's Kevin Breuninger contributed to this story.