Atlanta (CNN) When Pete Buttigieg got into the 2020 presidential race , his campaign was unknown, underfunded and hungry for any level of validation.

Months later, his outlook couldn't be more different.

Arguably more than any other Democratic presidential hopeful not named Joe Biden, the South Bend, Indiana, mayor has spent considerable time raising money at top-dollar, in-person fundraisers , crisscrossing the country to build a war chest big enough to fuel a campaign that has quickly -- and, in the eyes of even the mayor's top donors, unexpectedly -- jumped into the top tier of candidates just months after launching.

By the end of June, when the second fundraising quarter of 2019 closes, Buttigieg will have headlined roughly 70 in-person fundraisers, including 16 sizable "grassroots" events across the country that blend the size of a large campaign rally with the cash generation power of a fundraiser. Buttigieg, according to a campaign aide, now has roughly 20 full-time staffers working on fundraising, including those based in New York, California and the Washington, D.C., area.

"I have seen it change over time because eight weeks ago, there was no fundraising operation, as far as I could tell," said Rep. Don Beyer, a Virginia congressman and prolific Democratic fundraiser who endorsed Buttigieg in April. "It has come together really quickly."

All of it is set to pay off: A host of top Buttigieg donors who have been in regular contact with the campaign tell CNN that they expect the mayor to raise more than $15 million in the second quarter. The Buttigieg campaign set a goal of $15 million -- just more than double the $7 million it raised in the first quarter -- at the start of April, according to a source familiar with the strategy. But the quarter has been more successful than anticipated and the campaign is working to exceed its goal in the final 18 days.

A haul that size for a candidate who burst onto the scene mere months ago would be significant. Buttigieg's first quarter numbers placed him among the top handful of Democratic candidates . But a robust second quarter would elevate him into an even more enviable position among many of his rivals, some of whom are struggling to raise money.

While some candidates, like Vermont Sen. Bernie Sanders and Massachusetts Sen. Elizabeth Warren, are raising money almost exclusively online, Buttigieg's approach is far more aggressive, mixing online appeals with a particular focus on lengthy fundraising tours.

In May, Buttigieg headlined a three-day visit to California that included more than 10 fundraisers, including one hosted by actress Gwyneth Paltrow and actor Bradley Whitford. Buttigieg welcomed each guest as they arrived at Paltrow's home, according to one attendee, and smiled as the movie star introduced him as a candidate "who's got the brains."

He stood on the deck and answered questions for more than an hour, another attendee said, ranging from agricultural policy to the environment to immigration. Martin Sheen, who played President Josiah Bartlet on the television drama "The West Wing," was among those in the crowd, along with comedian Chelsea Handler and former US Deputy Attorney General Sally Yates.

An earlier event in California was hosted by Brian Goldsmith, an investor and college classmate of Buttigieg's at Harvard. Attendees included Cooper Hefner, the son of Playboy Founder Hugh Hefner and the company's chief of global partnerships; artist Alex Israel; Hollywood writer and producer Scoop Wasserstein; and Lauren Schuker, a writer, and her husband, Hollywood producer Jason Blum.

Buttigieg later in May headlined multiple events in New York and Chicago. And this week in the Washington area, Buttigieg has embarked on a three-day, six-event fundraising swing.

Buttigieg will close out the second quarter with a frenetic sprint of fundraising, first headlining a string of events in Los Angeles, including an event hosted by Nicole Avant, a Hollywood bundler who helped raise roughly $800,000 for then-Sen. Barack Obama in 2008, and a top-dollar fundraiser at the home of TV producer Ryan Murphy and his husband, David Miller, on June 19.

The mayor then will travel to Boston on June 20 for an event hosted by prolific political donor Jack Connors, where organizers hope to raise as much as $1 million, according to donors invited to the event.

Buttigieg campaign aides declined to comment on their prospective fundraising totals. But the mayor told reporters in Iowa this month that he was "cautiously optimistic" that he was going to post a strong number.

His aides contend that they have put an increased focus on fundraising this quarter because the mayor entered the presidential race without a significant donor base, especially when compared with his competitors.

"We are going up against people who have decades and decades of fundraising connections and experience and national networks," a campaign spokesperson said. "Pete came into this with no national fundraising network, and in a lot of instances he is meeting a lot for the first time, so we had to build a donor network."

The time spent fundraising doesn't come without cost, however, as every hour spent in a donor's living room in California or New York picking up $2,800 checks is time the mayor isn't in early nominating states.

The push and pull of fundraisers and events

Candidates have long struggled with how much time to spend on the campaign trail versus fundraising.

In 2016, Hillary Clinton's state-based operatives often quietly griped that the former secretary of state would have to leave an early-voting state to make a fundraiser, something they worried took her away from possible supporters.

Buttigieg has faced this conundrum, too. A campaign aide tells CNN that something they work in regularly is "a scheduling balance" between fundraisers and open events.

"We are making sure that we are hitting different cities and regions all around the country," the aide said.

To make up for days-long stretches on the fundraising circuit early in his campaign, Buttigieg's fundraising operation -- led by Anthony Mercurio, his director of investment, and Swati Mylavarapu, his campaign's investment chair -- began to plan grassroots events in the same cities as top-dollar fundraisers.

The grassroots events -- where would-be donors could pay as little as $25 to get in -- have more of a rally feel and are often filled with people who have never attended a campaign fundraiser before.

Steven and Sara Johnson stood on the second floor of Buttigieg's recent event in Atlanta, enjoying their first political rally. The couple had just had their first child and the Buttigieg event was their third date night since welcoming the new member of their family.

"You are donating to the campaign for the benefit of seeing him speaking," Steven Johnson said. "We didn't give it a second thought."

The campaign is seeing the same thing. According to the aide, 54% of the people at grassroots events are brand new to donating to the campaign.

To date, the campaign has hosted similar grassroots events in Minneapolis, San Francisco, Houston, Washington, New York, Boston and Miami. The events do not raise as much as some of the mayor's fundraisers, but, according to a source, Buttigieg's event in the Bay Area raised $140,000, which isn't an insignificant haul for him.

Campaign aides and donors are well aware that grassroots events, even if they bring around 1,000 people together, are not the same as town halls in Iowa or house parties in New Hampshire.

"There is always a tension between fundraising and campaigning," said Robert Zimmerman, a New York-based donor who has maxed out to Buttigieg. "At this stage, you can't have campaigning until you have a financial infrastructure in place. Frankly, he is doing both very effectively."

Rep. Beyer agreed, but said there will need to be a shift in strategy later this year.

"He is really spending a lot of time and energy to make sure he has enough resources to be credible," Beyer said. "Obviously, campaign leadership is going to have to find the right balance. It's fine in the short term, since he started out entirely shoestring and not having a finance base ... but I also believe after a good second quarter, a good third quarter, then he will have to shift focus back to the early states."

Unexpected growth

Early in the campaign, Buttigieg, who is gay, found himself leaning heavily on LGBTQ donors to propel his candidacy.

"It was especially important early on, when we were still trying to get known," Buttigieg said of LGBTQ donors on a recent trip to Iowa. "I think it helped us get that first look. And then, thankfully, when people take that first look, they like what they see and then we were able to broaden our base."

That process of getting donor validation was helped when the mayor became the darling of Democratic contributors after his performance at a CNN town hall in early March received sterling reviews. In the following days, campaign aides were flooded with operatives asking for jobs and countless top Democrats asking to host events for him.

The campaign looked to seize that momentum by booking a series of events, worried that, in a long campaign, this interest could run out at any time.

Three months later, that has yet to happen and Buttigieg's team remains in high demand among donors.

As Buttigieg's star has risen, his campaign has seen even more buy-in from LGBTQ donors, especially gay men.

"All the gay men I know, they all want to give him money," said Robby Mook, Clinton's 2016 campaign manager and the first gay man who ran a major presidential campaign. "It's not the worst demographic to raise money from."

That will be on full display when Bryan Rafanelli and Mark Walsh, two gay, longtime Democratic donors with deep ties to Bill and Hillary Clinton, host a top-dollar fundraiser for Buttigieg on July 5 in Provincetown, Massachusetts, a historically popular summer vacation spot for the gay community.

Celebrity interior designer Ken Fulk; Dan Mullin, a well-known Democratic donor who hosted events for Hillary Clinton; and Alix Ritchie, well known LGBT activist who is on the board of LPAC, and her spouse, Marty Davis, are co-hosting the event.

As one longtime Democratic donor, who is gay, told CNN: It's being considered "the gay party of the summer."

Such events demonstrate the shift in Buttigieg's fundraising strategy as he has gained popularity. Donors told CNN that the campaign once asked fundraiser hosts to raise around $25,000 at an event with the mayor. Those same donors said they won't even be considered to host a Buttigieg event now without guaranteeing a six-figure haul.

Beyer, who helped host an event for Buttigieg in the Washington neighborhood of Georgetown earlier this year, echoed this.

"It reminded me of early Obama," the congressman said. "It was the shooting fish in a barrel phenomenon, where everyone I called said yes. ... And then we ended up doing $300,000-plus at that event. It was his largest event to date. But we know that was a very short record."