South Bend, Indiana (CNN) South Bend Mayor Pete Buttigieg officially launched his presidential campaign on Sunday, formally vaulting the Midwestern Democrat who was largely unknown over a month ago into the large -- and growing -- field of Democrats vying to take on President Donald Trump in 2020.

Buttigieg cast his candidacy as a direct rebuttal to Trump's campaign -- including his slogan "Make America Great Again" -- and highlighted his belief that the country needs both a generational change and an entirely different political figure to lead the country past Trump. Buttigieg's argument is that he, a gay, veteran mayor from the Midwest, is just that kind of different politician.

"My name is Pete Buttigieg. They call me Mayor Pete," Buttigieg said to cheers. "I am a proud son of South Bend, Indiana. And I am running for President of the United States."

He said: "I recognize the audacity of doing this as a Midwestern millennial mayor. More than a little bold—at age 37—to seek the highest office in the land. ... But we live in a moment that compels us each to act."

The South Bend mayor is the fastest-rising Democratic candidate in the crowded presidential field and his decision to exit the lengthy exploratory portion of his 2020 bid comes at a time when a series of polls have shown Buttigieg to be firmly among candidates like Sens. Kamala Harris, Elizabeth Warren and Cory Booker, a far cry from when he was receiving less than 1% of support in some polls months ago.

His recent star power showed through in a flurry of donations after his announcement, with supporters contributing more than $1 million to Buttigieg's campaign in the four hours following his speech Sunday, his campaign communications adviser Lis Smith tweeted

Buttigieg used his hometown as a character in his announcement, including the fact that he, over the last eight years, had overseen a renewal in South Bend's city center.

"There's a long way for us to go. Life here is far from perfect. But we've changed our trajectory and shown a path forward for communities like ours. And that's why I'm here today. To tell a different story than 'Make America Great Again,'" Buttigieg said, the rain audibly beating down on the steel roof above him as the lectern in front of him visibly took on water. "Because there is a myth being sold to industrial and rural communities: the myth that we can stop the clock and turn it back."

He added: "It's time to walk away from the politics of the past, and toward something totally different. ... That's why, this time, it's not just about winning an election—it's about winning an era."

Buttigieg's launch took place inside the rain soaked and once bustling Studebaker plant that, when hollowed out after the company left in 1963, was a tangible symbol of his hometown's march toward decay. The building stood as a symbol of what Buttigieg hopes to deliver to the country: While the mayor announced on the rusted factory floor, just a doorway away stood the portion of the building that had been revitalized into a gleaming incubator to tech startups.

Buttigieg addressed a few hundred people in the event's outdoor and fully uncovered overflow area.

"I am impressed by the people standing inside," he said, the rain hitting his uncovered head. "I am moved by the people standing outside because this is what the beginning of a new American spring looks like."

It has been a whirlwind few weeks for Buttigieg: The mayor has crisscrossed the country looking to seize on the boost he received from a well-reviewed CNN town hall in early March, hopscotching between early nominating states and a string of fundraisers in Democratic strongholds like San Francisco, Chicago and New York.

By Buttigieg's own admission, the experience has been "heady," but now, the mayor said, it's time to make it official.

"What we've seen as we've explored is that we're exploring some really beautiful territory and now it's time to make it official and announce a decision," Buttigieg said on Friday as he made his way back to South Bend after a whirlwind trip through California that included an appearance on "Ellen" and a top dollar fundraiser in the Bay Area.

Buttigieg announced the exploratory committee at a January news conference in Washington, DC. He told CNN in late March that while, "all of the indicators are pointing" toward an official campaign, "a launch is something you only get to do once, and we're not going to do that until we have all of the pieces in place."

It wasn't always the plan to launch the campaign inside Studebaker's former factory. Initially, Buttigieg's nascent team has planned to basically shut down parts of South Bend's downtown and hold an outdoor rally in the heart of the city center that has been revived under the mayor's tenure. Rain and wind meant they had to change plans, but Buttigieg said there is a silver lining in the change.

"The rain location may be a blessing in disguise because there is such symbolic power in that building and you can see in it the past, the present and the future," Buttigieg said before the event. "I talk so much about how we're not looking to turn back the clock and it's not about retrieving some impossible again. That building is kind of a living symbol of all of that."

The building has recently been repurposed. It now anchors South Bend's Renaissance District and houses a mix of technology companies, including South Bend Code School and an Amazon Web Services company, a symbol of how his leadership as mayor over the last eight years helped revitalize portions of the city.

Buttigieg's speech covered a range of policy issues. The mayor called for sweeping Democratic reforms on voting and in the judicial system, called climate change "a life and death issue for our generation" and said he wants to make sure every American has access to Medicare.

But the best-received lines in Buttigieg's speech were when the mayor attacked Trump or spoke about his personal life, namely his marriage to Chasten Buttigieg.

The mayor spoke at length about wishing he could tell his younger self -- who wondered "what it means when he sometimes feels a certain way about young men he sees in the hall at school" -- that he would be accepted.

"To tell him that one rainy April day, before he even turns 40, he'll wake up to headlines about whether he's rising too quickly into becoming a top-tier contender for the American presidency. And to tell him that on that day he announces his campaign for president, he'll do it with his husband looking on," Buttigieg said to cheers.

He added earlier: "Our marriage exists by the grace of a single vote on the US Supreme Court. Nine men and women sat down in a room and took a vote and they brought me the most important freedom in my life."

Buttigieg cast Trump as a backward-looking politician who has looked to use fear as a way to gain power.

"The horror show in Washington is mesmerizing, all-consuming," Buttigieg said. "But starting today, we are going to change the channel."

Buttigieg was introduced on Sunday by three mayors -- Nan Whaley, the mayor of Dayton, Ohio; Christopher Cabaldon, the mayor of West Sacramento, California; and Steve Adler, the mayor of Austin, Texas -- all of whom highlighted a different aspect of Buttigieg's record and candidacy.

"Are we aware that we are making history," said Cabaldon, who himself is gay. "Even as the chair of America's LGBT mayors, I couldn't even dream of this moment four months ago."

Adler's endorsement was significant because two other Texans -- former Rep. Beto O'Rourke and former Housing and Urban Development Secretary Julián Castro -- are already running for president. Adler even spoke at an O'Rourke event earlier this year.

"I think you give consideration to endorse a lot of people. Beto is a really good guy. Julián is a really good guy. And they are both friends. Just not as close as Pete. The one that I have seen that is really the most spectacular is Pete," Adler said.

Although Buttigieg made his announcement official on Sunday, he officially dropped "exploratory" from his committee with the Federal Election Commission on Friday.

Buttigieg's committee has been shoestring for months. According to the Buttigieg aide, the committee currently has 32 people on staff and plans to get to 45 or 50 staffers by the end of the month.

That initially small staff has meant the mayor has spent very little of the $7 million his team raised in 2019's first fundraising quarter. According to the aide, Buttigieg's first quarter fundraising report will show he only has a burn rate of less than 10%, a number far smaller than other candidates, like Warren, whose campaign announced earlier this month her burn rate was more than 85%.

"Pete's a different kind of candidate and we want to build a different kind of campaign," said Mike Schmuhl, Buttigieg's campaign manager. "We don't want to a top down, consultant-laden operation. We want to be more like a startup, and we want to build in a smart way and a steady way."

Schmuhl said that, right now, the campaign does not have any pollsters or consultants. While he didn't rule them out in the future, Schmuhl said the campaign is looking to be "nimble as we go along."

The campaign has already opened a campaign headquarters in South Bend, two small suites in the Jefferson Centre building. The campaign also has plans to open a small office in Chicago, where a few aides will live and, given the relatively small size of South Bend's airport, the candidate and campaign aides will work ahead of flights around the country.

Buttigieg's rise has also seen him get accepted to the upper echelon of Democratic donors, many of whom are looking to donate to multiple candidates as the field continues to grow.

"I said to him I will do whatever you need. If it is raising money, I will raise money, if it is talking to people in the national network, I am all in," said Steve Grossman, a former DNC chair who endorsed Buttigieg days ago.

Another one of those donors is Susie Tompkins Buell, who -- while supporting Harris -- also hosted a fundraiser for Buttigieg and around 150 donors on Thursday in the Bay Area.

"He made a very big impression on, I think, everyone. He is very authentic, and this is what people are craving," she said. "That is one thing he has in common with the current president: What you see is what you get. Otherwise, they are complete opposites."

The mayor has also not been the only Buttigieg to experience a bump in notoriety. So, too, has Chasten Buttigieg, the mayor's husband and a teacher, who has become an omnipresent feature of political Twitter and, according to aides, is slated to do a number of solo speeches, primarily to LGBTQ and education groups.

Buttigieg will follow up his announcement with a trip to New York for a low-dollar fundraiser in Brooklyn on Monday, followed by a two-day trip to Iowa on Tuesday and Wednesday.