Abrams' endorsement is a major boost for Warnock out of the starting gates. Democrats hope to consolidate support around a single candidate in the race, particularly after Rep. Doug Collins (R-Ga.) launched his bid against Loeffler earlier this week, creating a major rift among Republicans.

In a tweet, Abrams called Warnock "a true ally in our fight for justice." She also plans to send out a fundraising email for him Thursday saying he has led on "issues of social justice, economic access and voting rights."

ENDORSEMENT TWEET: Reverend Raphael Warnock is a true ally in our fight for justice. That’s why I'm proud to endorse him for U.S. Senate here in GA. Take a moment to get to know him & if you can, chip in to support his campaign: https://t.co/c9tkvgYL2m #gasen #gapol https://t.co/GLyO5yKjmy — Stacey Abrams (@staceyabrams) January 30, 2020

"Georgia deserves a proven leader like Raphael Warnock — a son of South Georgia who knows our state inside and out — he’s traveled its highways, visited its towns and served its people for decades," Abrams says in the fundraising solicitation. A former state House minority leader who lost to Kemp in a competitive race for governor in 2018, Abrams was recruited to run for Senate this year against Sen. David Perdue (R-Ga.), but she spurned Democrats' entreaties — and also declined to run following Isakson's resignation.

Warnock also received support on Twitter from Sen. Cory Booker (D-N.J.), a former presidential candidate, and Sens. Sherrod Brown (D-Ohio) and Chris Murphy (D-Conn.) sent out fundraising emails on his behalf.

In a video announcing his campaign, Warnock spoke about his childhood in Georgia and his father's emphasis on hard work, as well as his work as the senior pastor at the church where Martin Luther King Jr. once preached.

"Some might ask why a pastor thinks he should serve in the Senate," Warnock said. "Well, I've committed my whole life to service and helping people realize their highest potential. I've always thought that my impact doesn't stop at the church door. That's actually where it starts."

The effort to unite around Warnock could complicate the campaigns of two other Democrats in the race or planning to enter it: Matt Lieberman, the son of former Sen. Joe Lieberman (I-Conn.), is already running, and former U.S. Attorney Ed Tarver has said he plans to run.

In an interview Thursday, Tarver said Warnock's announcement — and Abrams' endorsement — did not change his plans and that he still expected to formally launch his campaign in the coming weeks. He said the announcements were not unexpected, but that he and his team still believe they have a path to victory.

"I think one of the components of every election is that one candidate or the other is endorsed by prominent people and people who are less prominent. But the bottom line is voters will have their chance to make a decision," Tarver said.

If there are multiple candidates from each party on the ballot in November, it would likely guarantee a runoff in early January.