Former President Barack Obama has notably chosen to withhold his presidential endorsement, even as radical Sen. Bernie Sanders (I-VT) — who is too far-left to even call himself a Democrat — has been increasingly poised to take the nomination over Obama’s former running mate. But Obama’s high-profile former national security adviser is fine with making it official: She’s on board the Biden train.

In a tweet thread Monday, former national security adviser Susan Rice joined the likes of former Democratic candidates Pete Buttigieg and Sen. Amy Klobuchar (D-MN), who are reportedly throwing their support to Biden.

“I’m proud to endorse [Joe Biden] for President,” Rice announced online Monday.

“Here he is comforting me on 1/4/17 just after my mother passed away,” she wrote, along with a photo of Biden hugging her. “There is no one kinder, more empathetic and caring than [Joe Biden]. He will lead America with the same deep compassion and decency.”

“I worked very closely with [Joe Biden] for 8 years,” Rice explained. “He is smart, strategic and more experienced than any candidate in the field. No one is better prepared and more trusted by our allies to repair the incalculable damage Trump has done to our int’l standing and national security.”

“[Joe Biden] will bring dignity, integrity and normalcy back to the White House, restoring the soul of America and faith in our leaders and institutions,” she continued. “He is best equipped to work across the aisle to get Americans’ business done in Congress.”

She then underscored the aspect of his candidacy that most strongly recommends him: He’s got the best shot to win.

“Above all, [Joe Biden] is a Democrat and the strongest candidate to take on and defeat Trump,” she wrote. “That’s why Trump is so scared of Biden. Our fate as a nation depends on beating Trump. Nothing is more important, and now is not the time for risky bets or divisive revolutions.”

Biden, Rice argued, will also give the Democrats the best shot at taking the Senate. “With [Joe Biden] as our nominee, we have the best chance to expand the Democrats’ majority in the House and take back the Senate — so we can finally get stuff done. Every day, he will put the national interest above his personal interest. Please join me in supporting [Joe Biden].”

I'm proud to endorse @JoeBiden for President. Here he is comforting me on 1/4/17 just after my mother passed away. There is no one kinder, more empathetic and caring than @joebiden. He will lead America with the same deep compassion and decency. pic.twitter.com/4IBscj75VN — Susan Rice (@AmbassadorRice) March 2, 2020

@JoeBiden will bring dignity, integrity and normalcy back to the White House, restoring the soul of America and faith in our leaders and institutions. He is best equipped to work across the aisle to get Americans' business done in Congress. — Susan Rice (@AmbassadorRice) March 2, 2020

With @JoeBiden as our nominee, we have the best chance to expand the Democrats' majority in the House and take back the Senate — so we can finally get stuff done. Every day, he will put the national interest above his personal interest. Please join me in supporting @JoeBiden. — Susan Rice (@AmbassadorRice) March 2, 2020

While Obama is still refusing to publicly endorse Biden, he is reportedly working behind the scenes to boost him over Sanders, including by nudging Buttigieg to throw his support to the former Vice President now that he’s taken himself out of the race.

“Mr. Buttigieg talked with Mr. Biden and former President Barack Obama on Sunday night, according to a Democratic official familiar with the conversations,” The New York Times reported Monday. “Mr. Biden asked for Mr. Buttigieg’s support and the former mayor indicated he would consider the request. Mr. Buttigieg wants to sleep on the decision, he told aides, some of whom believe he should move quickly to endorse Mr. Biden.”

“Mr. Obama did not specifically encourage Mr. Buttigieg to endorse Mr. Biden, said the official, who insisted on anonymity to discuss private conversations,” the Times continues. “But Mr. Obama did note that Mr. Buttigieg has considerable leverage at the moment and should think about how best to use it.”

Buttigieg farewell address Sunday signaled that he would be backing a more centrist candidate over Sanders. “We need leadership to heal a divided nation, not drive us further apart,” he said. “We need a broad based agenda to truly deliver for the American people, not one that gets lost in ideology.”

Related: Democrats Face Three Scenarios With Sanders, And They’re All Bad