Since dropping out of the race for president, Sen. Cory Booker, said Sunday that he's not yet ready to make an endorsement in the Democrats' heated presidential primary.

I'm not sure," Booker said during an interview with ABC News' This Week. 

"Look, I'm literally still days — just days from stepping out of this race.

"I want to support a candidate that, yeah, wants to send [Senate Majority Leader] Mitch McConnell to the back benches, yeah, wants to beat Donald Trump, but also understands that beating Donald Trump is the floor — it's not the ceiling," Booker added.

Booker announced last Monday that he is dropping out of the Democratic presidential race, leaving just one Black candidate in the Democratic Primary.

"Nearly one year ago, I got in the race for president because I believed to my core that the answer to the common pain Americans are feeling right now, the answer to Donald Trump's hatred and division, is to reignite our spirit of common purpose to take on our biggest challenges and build a more just and fair country for everyone," Booker said in an email to supporters. 

"I've always believed that. I still believe that. I'm proud I never compromised my faith in these principles during this campaign to score political points or tear down others."

Booker's retreat means that Massachusetts Gov. Deval Patrick is now the only Black candidate remaining in the Democratic primary.

Trump responded to the news, tweeting, "Really Big Breaking News (Kidding): Booker, who was in zero polling territory, just dropped out of the Democrat Presidential Primary Race. Now I can rest easy tonight," he added. "I was sooo concerned that I would someday have to go head to head with him!"