Democratic megadonor Bernard Schwartz has started reaching out to party leaders, particularly House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer, to encourage them to back a candidate for president in order to stop the surge of Sen. Bernie Sanders.

Schwartz, the CEO of BLS Investments, told CNBC that in recent days he's been trying to speak with Pelosi and Schumer about making a pick, in the hope that voters will follow their lead and end up denying Sanders the party's presidential nomination.

"We should know who is the best person to beat Donald Trump, and with all due respect, Bernie Sanders cannot beat Trump," he explained, describing the message he has relayed to the two Democratic leaders.

Schwartz noted he has yet to hear back from them but insisted that, with Super Tuesday under a week away, party leaders have to take a stand now before Sanders captures the nomination — and, in his view, takes down the party.

"They have good political reasons not to endorse until the primary is over, but I think we are losing too much if we give up on this position," he added.

Although he isn't insisting on a particular candidate for Pelosi and Schumer to get behind, he said that he thinks the two best options, for now, are either former Vice President Joe Biden or former New York Mayor Mike Bloomberg, a billionaire funding his own candidacy for president. Schwartz is currently backing Biden's campaign for president.

Schwartz's concerns to leaders are being echoed by many Democratic leaders, including Bloomberg, whose campaign has ramped up its attacks on Sanders. There are also concerns among establishment Democrats that Sanders could hurt congressional candidates down the ballot if he were to be at the top of the party's ticket in November.

Representatives for Pelosi and Schumer did not respond to a request for comment. Both publicly signaled on Wednesday that they would be comfortable with Sanders leading the Democratic ticket in November.

Schwartz's links to Democratic leaders could move them in the direction he hopes they will go. He has been a key financier for congressional Democrats in the 2020 election cycle. He has donated over $885,000 to the House Majority PAC, a super PAC dedicated to helping Democrats get elected to the House of Representatives, while giving more than $620,000 to the Senate Majority PAC, according to the nonpartisan Center for Responsive Politics.

During the 2018 congressional midterms, Schwartz gave more than $3 million to Democratic causes. The New York Times reported in April that Schwartz was organizing dinners on how to handle Sanders' run for president with Pelosi, Schumer, former Gov. Terry McAuliffe of Virginia; presidential candidate former South Bend, Indiana, Mayor Pete Buttigieg and Neera Tanden, the president of the Center for American Progress.

Sanders is currently leading in two of the biggest states that are scheduled next week on delegate-rich Super Tuesday. In both California and Texas, Real Clear Politics polling averages show Sanders leading the field.

Sanders has also been picking up delegates in the buildup to the South Carolina primary. He dominated during the Nevada caucuses and squeaked out a victory in the New Hampshire primary after narrowly losing the delegate edge to Buttigieg in Iowa.