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Virginia Gov. Ralph Northam apologized Friday for appearing in a racially offensive photo on his medical school yearbook page that featured men in blackface and Ku Klux Klan robes. But a growing number of fellow Democrats and Republicans called on him to resign.

"Earlier today, a website published a photograph of me from my 1984 medical school yearbook in a costume that is clearly racist and offensive," Northam said in a statement. "I am deeply sorry for the decision I made to appear as I did in this photo and for the hurt that decision caused then and now."

He added, "This behavior is not in keeping with who I am today and the values I have fought for throughout my career in the military, in medicine and in public service. But I want to be clear, I understand how this decision shakes Virginians’ faith in that commitment.

"I recognize that it will take time and serious effort to heal the damage this conduct has caused. I am ready to do that important work. The first step is to offer my sincerest apology and to state my absolute commitment to living up to the expectations Virginians set for me when they elected me to be their Governor."

Five Democrats who have announced 2020 presidential runs or said they would form exploratory committees — Julián Castro, Sen. Kamala Harris, Sen. Cory Booker, Sen. Elizabeth Warren and Sen. Kirsten Gillibrand — said Northam should resign.

Harris, D-Calif, said it would take Northam's resignation to allow any healing to begin. "The Governor of Virginia should step aside so the public can heal and move forward together," she tweeted.

Booker, D-N.J., who officially launched his 2020 campaign Friday, tweeted: “We should expect more from our elected officials. He should resign."

Leaders are called to a higher standard, and the stain of racism should have no place in the halls of government. The Governor of Virginia should step aside so the public can heal and move forward together. — Kamala Harris (@KamalaHarris) February 2, 2019

The NAACP also called on the Virginia Democrat to step down. "Black face in any manner is always racist and never okay. No matter the party affiliation, we can not stand for such behavior," tweeted the organization's president, Derrick Johnson.

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New Jersey Gov. Phil Murphy, a fellow Democrat, said on MSNBC's "All in with Chris Hayes" that Northam doesn't seem to have a choice other than to resign.

"I know him and I think he’s a good man, but as you said earlier, it is disqualifying," Murphy said of the photo. "Particularly at this time, with the division in this country.”

Northam was resisting those calls Friday night. He tweeted out a video of his apology, but added that he had promised to fight for Virginia, and "I'm committed to continuing that fight through the remainder of my term."

BREAKING: "I don't see that the governor has any other choice but to step aside," New Jersey Gov. Murphy tells @chrislhayes after revelation of Virginia Gov. Northam in racist 1980s yearbook photo. pic.twitter.com/N2Bwl57Pjl — MSNBC (@MSNBC) February 2, 2019

The photo from the 1984 Eastern Virginia Medical School yearbook ran alongside pictures of and personal information about Northam.

NBC verified the yearbook pictures with the school. NBC is not aware of the identities of both of the men in the picture in blackface or the Klan robes — although the governor's statement confirms he is one or the other — but all the other photos on the page are clearly of Northam: one in a suit jacket, one in a cowboy hat where he is holding a beer, one sitting next to a Corvette.

Vincent Rhodes, chief communications officer for the school, said the production of the yearbook was a student activity, adding, "We don’t know when or where the picture was taken and we don't know anything about its content."

Virginia Gov. Ralph Northam, center, speaks about the Virginians for Reconciliation and Civility proclamation during a press conference inside the Pocahontas Building in Richmond, Virginia on Jan. 16, 2019. Bob Brown / Richmond Times-Dispatch via AP

"Racism has no place in Virginia," said Republican Party of Virginia Chairman Jack Wilson in a statement before Northam apologized. "These pictures are wholly inappropriate. If Governor Northam appeared in blackface or dressed in a KKK robe, he should resign immediately."

The Virginia Legislative Black Caucus issued a blistering statement that stopped short of calling for Northam's resignation. "We are still processing what we have seen about the Governor but unequivocally say that what has been revealed is disgusting, reprehensible, and offensive. We feel complete betrayal," the statement said.

Julián Castro was the first 2020 Democratic presidential candidate to call on Northam to step down after his apology.

"It doesn't matter if he is a Republican or a Democrat. This behavior was racist and unconscionable. Governor Northam should resign," he tweeted.

Three Democratic California congressmen, Eric Swalwell, Ted Lieu and Ro Khanna, separately called for Northam to go, with Khanna noting the photo emerged on the first day of Black History Month.

"Northam should accept responsibility & resign paving the way for Lt. Gov Justin Fairfax to become the second African American governor in Virginia's history. That is the type of restorative justice that our nation cries out for at this time," Khanna tweeted.

The executive director of MoveOn.org, a progressive group, also demanded his resignation.

And now @RalphNortham’s response is unacceptable. He must resign immediately. Period. https://t.co/bNralsfDUE — Ilya Sheyman (@iSheyman) February 2, 2019

Northam, a doctor, came under fire from Republicans earlier this week, who accused him of supporting infanticide because of comments he made in support of allowing late-term abortions when the fetus is severely deformed or would be unable to survive after birth.

He was elected governor in 2017 in a hotly-contested race against Republican Ed Gillespie. Northam said he supported taking down Confederate monuments, a stance Gillespie blasted him for.

In his victory speech, Northam, an Army veteran and pediatric neurologist, said, "Virginia has told us to end the divisiveness, that we will not condone hatred and bigotry."

"It’s going to take a doctor to heal our differences. And I’m here to tell you, the doctor is in!" he declared.

The yearbook photo was first reported by Big League Politics, a far-right website that often promotes conspiracy theories.