As Kamala Harris events fill up, democratic megadonors intensify their calls for Biden to withdraw from the race.

• Congressional leaders are being pressured by donors who fund the Biden campaign to drop out.
• The former Secretary of State, her husband, the former President, and the Biden campaign co-chair and media mogul have all appealed to donors, urging them to remain committed to Biden.
• Sell-out events featuring Vice President Kamala Harris, who is expected to succeed Biden if he chooses to step down, have begun to occur.

A Zoom call was held on a Tuesday in early July by 75 wealthy Democratic political donors to discuss the future of President Joe Biden after his poor debate performance against Donald Trump, as reported by a call participant.

One donor out of the group said that Biden should stay in the race, while the others were adamant that he needed to drop out in order for the party to defeat Trump in November. Sources who spoke to CNBC for this story were granted anonymity to discuss a sensitive matter.

Big money donors have launched a lobbying campaign aimed at senior Democrats in both the House and Senate since then.

Over half a dozen people familiar with the matter claim that their goal is to persuade lawmakers to publicly urge Biden to abandon his reelection campaign.

Several donors made it clear that they would not contribute to Biden's reelection campaign unless he dropped out, and they would only resume donations once polls indicated that he was leading Trump.

According to two sources, Hollywood executive Ari Emanuel, his brother Zeke Emanuel, and Alan Jones, a senior managing director at Intermediate Capital Group and a longtime Democratic party donor, are among those who have made calls to Democrats on Capitol Hill.

Some of Biden's allies tried to prevent donors from leaving his team after the effort was made.

According to sources, Hillary Clinton, Bill Clinton, and Jeff Katzenberg have all appealed to donors, urging them to remain loyal to Biden.

Despite over 20 members of Congress urging him to "pass the torch," Biden has consistently stated that he has no intention of withdrawing from the presidential race.

One longtime Biden bundler stated that almost every donor has privately or publicly expressed their deep concern to the campaign team, Pelosi, Schumer, and Jeffries.

The bundler stated that although Biden is not concerned with donors' opinions, the leadership takes their views into account due to the potential influence on down-ballot races.

Biden has been reportedly cautioned by Pelosi, Schumer, and Jeffries about their members' concerns and the potential negative impact on congressional candidates if he continues his presidential campaign.

The Biden campaign, as well as representatives for Hillary and Bill Clinton and Zeke Emanuel, did not respond to requests for comment from CNBC. Additionally, a press representative for Ari Emanuel declined to comment. Jones also did not respond to emails seeking comment.

Yet Biden's fundraising collapse does not necessarily spell doom for the party.

Events featuring Vice President Kamala Harris, who is expected to succeed Biden if he chooses to step down, have begun to sell out.

The concert event in Pittsfield, Mass. on July 27 featuring James Taylor and Yo-Yo Ma is almost entirely sold out, with tickets starting at $100 and going up to just over $12,000, according to the invitation.