Former Texas Congressman Beto O'Rourke speaks to a crowd of marchers during the anti-Trump 'March for Truth' in El Paso, Texas, on February 11, 2019.

One of former U.S. Rep. Beto O'Rourke's supporters from his 2018 Senate campaign has been reaching out to top Democratic Party donors to see if they will back him to run for president in 2020.

Louis Susman, former U.S. ambassador to the U.K. and a lead bundler for Barack Obama's first presidential campaign, has been speaking with political financiers from across the country, including those in the financial industry, to see if they will invest in O'Rourke's campaign, according to people with direct knowledge of the outreach.

The former Obama backer has put together a string of senior party donors who are willing to contribute to the former congressman's presidential operation, said the people, who declined to be named due to the conversations being deemed private.

In an interview with CNBC, Susman says the people he's talked to about donating to the campaign are "family and friends." He added "everyone is excited to go," while noting he's been in touch with O'Rourke's campaign and coordinating his efforts with them. He declined to say who these donors are or which industry they are from.

"Whatever I do, I do it in coordination with the campaign," Susman said. He said there's no discussion about him becoming a campaign finance chairman and he has not recently spoken with O'Rourke himself. He's confident the former Texas Senate candidate will be successful in the fundraising circuit.

"I don't think, whether it's through large bundlers or small donors, that he's going to have a tough time raising money," Susman said.

He also did not rule out holding fundraisers for O'Rourke, noting "everything is in the planning stages."

"The team is focused on these four days in Iowa, and everything is going to develop from there," he added and then abruptly ended the phone call.

Meanwhile, his daughter, Pfizer executive Sally Susman, is supporting another 2020 hopeful: Sen. Kirsten Gillibrand of New York. She's hosting a fundraiser for Gillibrand in March at her home, and tickets range from $1,000 to $2,700.

CNN first reported in December that Louis Susman was planning to support O'Rourke's candidacy if he ran for president.

A spokesman for O'Rourke did not return repeated requests for comment.

O'Rourke officially launched his campaign for president on Thursday and declared he would be following the same pledge he made when he ran for a Senate seat from Texas in 2018: He will not accept contributions from political action committees, corporations or any special interests. He did not rule out receiving the backing of wealthy financiers like Susman, who currently is a senior advisor to behemoth asset management firm Perella Weinberg Partners and investment firm Atlas Merchant Capital.

Susman was a contributor to O'Rourke's failed Senate bid, in which he lost to Ted Cruz by just under 2 percentage points. He wrote a $2,700 check to O'Rourke's campaign in March 2018. O'Rourke finished the 2018 election cycle raising $80 million with almost half of the contributions coming from supporters who gave $200 or less.

For O'Rourke, having Susman on his side could prove to be a difference maker, especially in appealing to donors who are willing to write the larger checks.

"Here's what Beto doesn't know: if the contributions he got in Texas will translate into a presidential race. He doesn't know that," said a Democratic donor who's heard Susman's pitch for backing O'Rourke. "He can't just rely on that if he really wants to win," this source added.

Before becoming Obama's ambassador, Susman bundled at least $500,000 during Obama's first run for president in 2008, according to the nonpartisan Center for Responsive Politics. He was also the national finance chairman for John Kerry's 2004 bid for president.