The president tested positive for COVID-19 Wednesday afternoon, the White House said.

Biden is experiencing "mild symptoms," White House press secretary Karine Jean-Pierre said in a statement.

Biden was campaigning in Las Vegas and attended one event earlier in the day, according to Jean-Pierre.

"He will be returning to Delaware where he will self-isolate and will continue to carry out all of his duties fully during that time," she said.

The White House doctor provided more details, stating Biden had a runny nose, "and non-productive cough, with general malaise." The president's temperature was 97.8 degrees and he had taken his first dose of Paxlovid, the doctor said.

-ABC News' Justin Fishel

Minnesota Gov. Tim Walz, the co-chair of the DNC Rules Committee, called Biden campaign chair Jen O'Malley Dillon on Tuesday to push for the delay of the virtual roll call that would officially nominate Biden, two people with direct knowledge of the call told ABC News.

Walz co-wrote the letter sent this morning to rules committee members, which set the proposal for an early August virtual nomination of Biden. The roll call could previously have been held as early as Sunday.

Walz told O'Malley Dillon that he has been hearing from other governors who want the roll call to be pushed back. The Biden campaign made the concession to push it back, one source said, and even helped to propose the solution.

Walz's efforts were separate from those of House Minority Leader Jeffries and Senate Majority Leader Schumer, the source said.

-ABC News' Isabella Murray

Senate Majority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries pushed the party to delay its nominating process, multiple sources tell ABC News.

This comes after Schumer met privately with President Biden on Saturday in Rehoboth, Delaware. Following the meeting, Schumer only described it as a "good meeting."

This is the biggest indication so far that Schumer is keeping an open mind about Biden's future.

Schumer and Jeffries spoke and both agreed to make the push, according to the sources.

-ABC News' Rachel Scott and Allison Pecorin

Vice President Kamala Harris on Wednesday accepted a third date option proposed by CBS News for a vice-presidential debate, a Biden campaign official said.

The new proposed date is for Monday, Aug. 12, according to the Biden campaign.

"Now that the Trump campaign has selected a running mate, we encourage them to agree to a debate between Vice President Harris and Senator Vance," the campaign official said.

On May 16, CBS News offered two debate date options on either July 23 (the week after the RNC) or Aug. 13 (the week before the DNC), which Harris accepted at the time.

The next day Trump accepted a Fox News proposal for his eventual running mate -- who we now know is Vance.

"On behalf of the future Vice President of the United States, who I have not yet chosen, we hereby accept the Fox Vice Presidential Debate, hopefully at Virginia State University, the first Historically Black College or University to host a Debate - Date to be determined," Trump posted on Truth Social at the time. "I urge Vice President Kamala Harris to agree to this. MAKE AMERICA GREAT AGAIN!"

Fox News’ VP debate offer was for the same dates CBS News originally offered.

-ABC News' Fritz Farrow, Gabriella Abdul-Hakim and Will McDuffie