By Scott Wong and Mike Lillis, The Hill–

Sen. Cory Booker (D-N.J.) on Thursday began calling members of Congress informing them he is running for president and is quietly making overtures to members for support, three congressional sources told The Hill.

“Yes, he is reaching out to members for their support,” said a former Democratic aide with direct knowledge of Booker’s intentions. “He’s going to do it during Black History Month,” which starts on Friday.

“I don’t know if it’s going to be tomorrow, I just know it’s going to be soon.”

Among those who received a call Thursday were senior members of the Congressional Black Caucus (CBC), of which Booker is a member.

“He’s making calls,” a fourth source, Rep. Frederica Wilson (D-Fla.), confirmed to The Hill on Thursday night. “He left me a voice message. I have to call him back.”

A Booker spokesman declined to comment for this story.

Booker’s entry into the 2020 Democratic presidential primary race was widely expected, but his announcement on the heels of the successful presidential launch of Sen. Kamala Harris (D-Calif.) suggests he and his team realized he could not allow his Senate colleague and fellow CBC member build too much momentum, some Democratic observers said.

Both Booker, 49, the former mayor of Newark, and Harris, 54, the former California attorney general, have been vying for endorsements from CBC members – a sign of the importance of the black vote in the Democratic primary, especially in states like South Carolina, Ohio and Georgia.

On Wednesday, both Booker and Harris attended the CBC’s annual policy retreat for more than an hour. Though their 2020 presidential bids were not the focus, both senators worked the room during breaks.

More than a dozen CBC members interviewed by The Hill said they were not ready to endorse anyone in yet with the 2020 field continuing to take shape.

As he left the meeting in the Capitol’s basement, Booker sidestepped a question about whether he felt any pressure to quickly launch a presidential bid now that Harris had begun to win congressional endorsements from lawmakers in her home state.

“I’m excited for the candidates already out there. It’s really good for the Democratic Party and it’s just a good thing,” Booker told The Hill. “I’m excited about Kamala’s candidacy. It’s incredible. It’s historic.”

The former Democratic aide said Booker will have a leg up on Harris with CBC members, because he’s been a more active member of the group.

“He rarely misses a CBC meeting,” the former aide said. “Kamala Harris – great member – but that’s just not her thing. … So I could easily see Cory Booker getting more of their support.”

The aide compared the situation to 2008, when Obama thought he’d lock down the support of CBC members because he was a part of the group. “But he never went to a CBC meeting,” the former aide said, which allowed Hillary Clinton to gain the support of much of the caucus.

“Cory Booker has invested in the CBC relationships.”

If Harris wins the nomination and defeats President Trump, she would become the first female to win the White House and the second African American after Barack Obama.

The Democratic primary is expected to be crowded, however. Aside from Harris and Booker, Sens. Elizabeth Warren (D-Mass.) and Kirsten Gillibrand (D-N.Y.) are already running. So are Rep. Tulsi Gabbard (D-Hawaii), former Rep. John Delaney (D-Md.), former Housing and Urban Development Secretary Julian Castro and Pete Buttigieg, mayor of South Bend, Ind.

“The field isn’t even half full yet,” one Democratic senator quipped.