Former Vice President and 2020 Democratic presidential candidate Joe Biden, center, poses for selfies with bartenders during his visit to the Stonewall Inn, Tuesday, June 18, 2019, in New York.

Democratic donors from across the country have been holding fundraising events and meetings for months trying to figure out who their preferred candidate is to take on President Donald Trump.

While they haven't decided on a favorite, many financiers have put their resources behind former Vice President Joe Biden, Sen. Kamala Harris of California and South Bend, Indiana, Mayor Pete Buttigieg.

All three have been taking part in fundraising events in some of the bigger coastal cities, such as New York, Boston, Los Angeles and San Francisco, where many fundraisers take place and influential bundlers reside.

Privately, party donors have expressed to each other a wide range of reasons for their interest in assisting these candidates.

Some donors see Biden as part of the old guard who has the potential to bring the country together after what some believe is a divisive Trump presidency.

Buttigieg, on the other hand, is appealing to financiers who argue it is time for a change in the party's leadership — and that he acts like the kind of nonpolitician who could take on Trump.

Harris is seen as a consistent winner who is so determined to defeat Trump that she could be willing to be the vice presidential candidate if she doesn't win the top spot.

Marc Lasry, a New York-based hedge fund manager and co-owner of the NBA's Milwaukee Bucks, hosted a fundraiser for Harris on Tuesday, he confirmed to CNBC's "Halftime Report." The goal of the gathering, CNBC reported, was to raise up to $200,000 for her campaign. Yet she came just short of that goal, people familiar with the matter said.

Even though Lasry said he had contributed to multiple candidates, he indicated to be all in on helping Harris win the fundraising game and possibly the nomination.

"Right now, I think she's probably the best candidate. So, I like her. Look, I think you need to have somebody who has some new ideas. I think ultimately, at the end of the day, she should be the nominee," he told CNBC.

That night, Biden was hosted by former hedge fund executive Eric Mindich and was surrounded with some of Wall Street's biggest donors. That list included Roger Altman, founder of Evercore; Stephen Scherr, chief financial officer at Goldman Sachs; Steve Rattner, chief executive officer of Willett Advisors LLC; and Robert Rubin, a former Treasury secretary under President Bill Clinton who is now at investment firm Centerview Partners.

Biden's New York fundraising blitz, which included a gathering at the home of short seller Jim Chanos, was estimated to bring in $1 million, according to people familiar with the matter.

A few of the people who went to the Biden event are also helping Harris and Buttigieg behind the scenes, according to people who spoke on the condition of anonymity.

Rubin's appearance was a surprise, since he is known in donor circles to have rarely attended fundraisers this cycle — leading to speculation that he has decided to back Biden. Rubin has acted as an outside advisor to presidential candidates.

While donors who attended the Biden and Harris events were impressed with the contenders, the one candidate donors can't seem to get enough of is the South Bend mayor.

"Everybody is talking about Buttigieg. He's young and he's dynamic," said an attendee of a Biden fundraiser who spoke on the condition of anonymity due to being friends with members of the former vice president's campaign.

"Buttigieg is a very impressive guy, and there's a lot of true generational shift in him," a senior contributor said.

A spokesperson for Biden declined to comment. Rubin and representatives of the Buttigieg and Harris campaigns did not return requests for comment.