Minnesota Rep. Angie Craig also became the first incumbent in a tight race to do so, saying, "I do not believe that the President can effectively campaign and win against Donald Trump."

Coupled with reports that Senate intelligence committee chair Mark Warner is point man in a drive to organize Senate Democrats into a united front urging Biden to quit, the political pressure is clearly mounting. However, Biden is also under rapidly-rising pressure along a second front, as major Democratic donors are not only telling him to quit, but are closing their checkbooks -- or creatively using them to pave the way for a new candidate. 

One of those deeply-disenchanted donors is Netflix co-founder Reed Hastings, who gave more than $20 million to boost Democratic candidates in recent years, including upwards of $1.5 million for Biden's 2020 campaign. Last week, Hastings publicly called for Biden to quit. He reiterated that stance after watching Biden's terrible Friday interview with George Stephanopoulos, telling ABC News. "Biden is unfortunately in denial about his mental state. He needs to step aside to let a vigorous Democratic leader beat Trump."

Then there's Kase Capital Management portfolio manager Whitney Tilson, who told ABC, "[Biden]'s not in [a] condition to handle the rigors of the presidency for another four years...All of us are standing by to see what happens here. Even the wealthiest people have limitations to money." More bluntly, he took to Twitter to say, "Biden's campaign is a ghost. It's over." 

Rather than simply moving to the sidelines, some mega-donors are engaging in creative political-financial engineering -- such as former Inuit and Paypal CEO Bill Harris, who donated $620,000 to the Biden Victory Fund in 2020 and told ABC that, given his performance in the debate and the Stephanopoulos interview, most observers would see Biden's departure as "inevitable."

On Friday, Harris announced that his Democrats for the Next Generation PAC was committing to spend $2 million "to fund a series of debates among prominent candidates to become the Democratic nominee for president if Biden steps aside." Some are referring to the concept as a "mini-primary" -- and it's seen by many as a mechanism for ensuring that Kamala Harris isn't tapped merely by virtue of her title.  

Bill Harris waved off Democrats' unease about a potentially messy and divisive process for picking a new candidate. "It's not that we have to protect ourselves from chaos and drama," Harris told the Washington Post. "We need drama and a little chaos. I think it can be refreshing and energizing."