Barack Obama reportedly intends to intervene to keep Bernie Sanders from becoming the Democratic presidential nominee.

According to Politico, the former president privately told his advisers that he would speak up if Sanders started running away with the nomination. Obama's spokesperson didn't confirm the report but pointed to what could happen if Sanders gets a sizable lead in the race for the nomination. 

“I can’t really confirm that,” Obama's adviser told Politico. “He hasn’t said that directly to me. The only reason I'm hesitating at all is because, yeah, if Bernie were running away with it, I think maybe we would all have to say something. But I don't think that's likely. It's not happening.”

The former president has reportedly said he won't go against any Democratic nominee, seeing his only role in the primary as “providing guardrails to keep the process from getting too ugly and to unite the party when the nominee is clear.”

However, Sanders could be the potential exception. An Obama adviser also reportedly told Politico “Bernie’s not a Democrat.”

The 58-year-old former president expressed his support for the nominees at a recent Democracy Alliance event in Washington, HuffPost reports. 

“Look, we have a field of very accomplished, very serious and passionate and smart people who have a history of public service," Obama said. "Whoever emerges from the primary process I will work my tail off to make sure that they are the next president.”

According to Politico, Obama has also been privately criticizing other nominees. The former president reportedly has doubts about Kamala Harris’ appeal to African Americans, remains “deeply skeptical” about Pete Buttigieg’s chances and has concerns about Joe Biden's bond with the electorate, especially in Iowa.

Biden was reportedly disappointed because Obama didn't give him an endorsement.

According to a Quinnipiac University national poll released Tuesday, the former vice president has taken the lead again in the primary race while Senator Elizabeth Warren’s support has declined. Biden has 24% of the vote among Democratic voters and independent voters who lean Democratic, while Buttigieg gets 16%, Warren has 14% and Sanders follows with 13%.