California Governor Gavin Newsom, acting as a surrogate for President Biden following Thursday night’s debate, once again deflected questions over whether he might potentially replace Biden on the Democratic ticket.

“No, our nominee is Joe Biden,” Newsom told reporters. “I’m looking forward to voting for him in November.”

Calls for Biden to step aside intensified after the president’s lackluster performance Thursday night with prominent Democrats now openly expressing concern that he can no longer lead the party to victory over Donald Trump in November.

“I’m not the only one whose heart is breaking right now. There’s a lot of people who watched this tonight and felt terribly for Joe Biden,” former Democratic Sen. Claire McCaskill said on MSNBC. “I don’t know if things can be done to fix this.”

Newsom, a former San Francisco mayor and lieutenant governor, urged Democrats not to panic.

“I think it’s unhelpful. And I think it’s unnecessary. We’ve got to go in, we’ve got to keep our heads high,” Newsom told MSNBC. “We’ve got to have the back of this president. You don’t turn back because of one performance. What kind of party does that?”

Newsom’s repeated denial that he is running a shadow campaign, however, has not quelled speculation.

Do you think Newsom could defeat Trump? Cast your vote below:

Poll not displaying? Tap here.

Every state has already held its presidential primary. Democratic rules mandate that the delegates Biden won remain bound to support him at the party’s upcoming national convention unless he tells them he’s leaving the race.

Biden indicated that he had no plans to do that, telling supporters in Atlanta shortly after he left the debate stage, “Let’s keep going.” Biden campaign spokesperson Lauren Hitt was even clearer, saying Friday: “Of course he’s not dropping out.”

The political parties control the conventions and their rules. The Democratic National Committee could convene before the convention opens on Aug. 19 and change how things will work, but that isn’t likely as long as Biden wants to continue seeking reelection.

The current rules read: “Delegates elected to the national convention pledged to a presidential candidate shall in all good conscience reflect the sentiments of those who elected them.”

What about Vice President Kamala Harris?

The vice president is Biden’s running mate, but that doesn’t mean she can swap in for him at the top of the ticket by default. Biden also can’t decree that she replace him should he suddenly decide to leave the race.

The Democratic National Convention is being held in Chicago, but the party has announced that it will hold a virtual roll call to formally nominate Biden before in-person proceedings begin. The exact date for the roll call has not yet been set.

If Biden opts to abandon his reelection campaign, Harris would likely join other top Democratic candidates looking to replace him. But that would probably create a scenario where she and others end up lobbying individual state delegations at the convention for their support.

That hasn’t happened for Democrats since 1960, when John F. Kennedy and Lyndon B. Johnson jockeyed for votes during that year’s Democratic convention in Los Angeles.

The Associated Press contributed to this report.