President Biden’s COVID symptoms have "improved significantly," according to his doctor, who made no specific mention of the president’s cough or hoarseness as he did in his previous updates.

Biden took his eighth dose of Paxlovid on Sunday morning, Dr. Kevin O’Connor said.

“His pulse, blood pressure, respiratory rate and temperature remain absolutely normal. His oxygen saturation continues to be excellent on room air. His lungs remain clear," O’Connor said. "The President continues to tolerate treatment without any difficulty and will continue PAXLOVID as planned."

-ABC News' Justin Ryan Gomez

With calls growing for President Joe Biden to , ABC News has learned more about how the Trump campaign is preparing for a scenario in which Vice President Kamala Harris becomes the Democratic nominee for president.

The Trump campaign is preparing new ads to attack Harris' record, and is compiling opposition research books and conducting polling to test her weaknesses in a general election matchup, sources familiar with the plans tell ABC News.

Read more here.

In a Wall Street Journal op-ed Sunday, Rep. Dean Phillips, D-Minn. and former long-shot Democratic presidential candidate, called on Congressional Democrats to hold a confidence vote on President Joe Biden as the party's nominee.

Phillips said that this method would be democratic, because those lawmakers were elected by Americans across the country.

"That’s why I believe House and Senate Democrats, directly elected by voters from across the country, must hold an immediate vote of confidence and share the results directly with Mr. Biden," Phillips wrote in the op-ed. "It can be done by secret ballot, as fear of political retribution still prevents many members from speaking publicly. But a poll of elected Democrats whose electoral fates are closely tied to the president is far superior to one of unelected members of the Democratic National Committee."

If the vote of "confidence" wins, then Democrats should coalesce their support behind the president, Phillips wrote.

"But if ‘no confidence’ is the consensus, the president must end his candidacy," he added.

In the case of a "no confidence vote," Phillips said he thinks Vice President Kamala Harris would become the party's candidate, but Phillips proposed a method to selecting the party's ticket.

"The president and the party could then either endorse and elevate Vice President Kamala Harris to the top of the ticket or promote a one-month ‘miniprimary,’” he wrote.

Phillips also called on Biden to "pass the torch" during an interview on CBS' "Face the Nation" on Sunday.

Sen. Joe Manchin, I-W.Va., who caucuses with Democrats but left the party earlier this year, told "This Week" co-anchor Martha Raddatz on Sunday that he came to the decision "with a heavy heart," but that the swell of Democrats issuing similar calls after last month's debate made the current situation untenable for President Biden.

Manchin argued that dropping out now would allow Biden to tackle a litany of issues he's prioritized, including uniting the country, ending fighting in Gaza and helping Ukraine fend off Russia's invasion, on top of being "able to show the rest of the world the orderly transfer of power from the superpower of the world."

"He will go down with a legacy unlike many people, as one of the finest and truly a [patriotic] American," Manchin said. "So, with that, I come with a heavy heart to think the time has come for him to pass the torch to a new generation."

Read more here.

-ABC News' Tal Axelrod