MIAMI—Marco Rubio has declared that yesterday is, well, buried in the past.

From a stage here at the Freedom Tower, steeped in cultural, biographical and political symbolism for this newly minted presidential candidate, the son of Cuban immigrants declared his bid for the White House on Monday evening.

Rubio rooted his campaign in an American Dream narrative (his parents were a bartender and a maid) and his youth—attributes he believes will set him apart from his Democratic and Republican rivals, including his political mentor and fellow Floridian Jeb Bush.

The freshman senator from West Miami described the presidential race of 2016 as “a generational choice about what kind of country we will be."

In a contest that could ultimately pit two political dynasties against each other—Bush and Clinton—Rubio made clear he is hoping to disrupt that possibility.

"Yesterday is over, and we are never going back,” he said, flanked by his wife, four children and a stage full of family members. “Before us now is the opportunity to author the greatest chapter yet in the amazing story of America. We can’t do that by going back to the leaders and ideas of the past. We must change the decisions we are making by changing the people who are making them." The line drew raucous applause.

The 43-year-old Florida lawmaker, who upended the status quo in his 2010 race for the Senate, is not the only young candidate hoping to win the White House. Ted Cruz and Scott Walker are also under 50, and each of those political upstarts hopes to draw sharp contrast between himself and likely Democratic nominee Hillary Clinton. But Rubio moreover aims to provide a demographic appeal his party needs.

The senator's event here had the feel of a neighborhood crowd beaming with pride in cheering on a hometown son. It was among the most diverse groups ever gathered for a Republican presidential launch; many could be heard speaking Spanish, some wore "Viva Marco" pins on their lapels, and many were dressed up for the evening event.

Rubio has a successful track record taking aim at lofty goals. Aversion to risk doesn’t seem to be part of his DNA. But there is no political battle like a presidential race, and this challenge will be the riskiest of his life. Rubio has said he would not seek re-election to his Senate seat in 2016 if he ran for the Oval Office. Taken at his word, a failed presidential bid would leave him without a political office come January 2017. Conceding his Florida seat in a presidential election year also puts it at risk for the GOP, which could upset party operatives hoping to hold on to the upper chamber.

He’s still young, of course, and could always try again. But as Rubio well knows, there may not be better moment ahead than the one in front of him now: The Republican Party is struggling to diversify and needs to modernize its message, especially among Latino and young voters; it also will likely face a Democratic nominee whom opponents regard as a relic of the past.

His well-received speech earned its most enthusiastic response when he noted, “I have heard some suggest that I should step aside and wait my turn. But I cannot. Because I believe our very identity as an exceptional nation is at stake, and I can make a difference as president.” The crowd chanted back, “It’s your turn!”

Rubio’s birthplace of Miami and his handle on the diverse and delegate-rich state of Florida might in any other race have him leading the GOP pack right now. But another Floridian, a former governor of the state with a powerful last name, record, and fundraising arm, threatens to turn this competition into David and Goliath tale. Of course, in that parable, the underdog wins. It’s not clear yet, though, whether Rubio can match the well-connected Bush’s support.

Each has been respectful when referencing the other, but both have started downplaying the significance of their once strong relationship. (When Rubio became state House speaker, Bush said, “I can’t think back on a time when I’ve ever been prouder to be a Republican, Marco.” When Rubio thought about running for Senate, he said he would defer to Bush if he wanted to run.)

But that was then.

“It’s going to be a bloodbath,” said Luz Gonzales, an educator from Miami waiting in line at the Freedom Tower to hear Rubio on Monday. Gonzalez said Bush was a good governor, but his support for Common Core education standards puts him towards the bottom of her list. Rubio, she says, “gets” the middle class. And his penchant for refusing to wait his turn resonates with her.

“The idea of the elite and waiting you're turn while the establishment determines who the next candidate is going to be--that is over,” Gonzales said. “That period in the Republican Party is absolutely over.”

The generational divide is what appealed to Caleb Parker, a Cleveland native and freshman at Gettysburg College in Pennsylvania who came to Miami to see Rubio launch his campaign. “I just don't think Jeb Bush has the passion behind him that Marco Rubio has,” Parker said. “Rubio shows how the American Dream is still achievable today; you don't have to come from money or a strong economic background to achieve what you want to achieve.”

Rubio is attempting to attract conservatives and Tea Party types while also convincing the party’s rank-and-file that he is a formidable force. But that task is a challenging one. Wisconsin Gov. Scott Walker is also trying to navigate both lanes and doesn’t have a record of Washington experience and controversial legislation -- like the failed immigration reform bill Rubio briefly got behind last year -- to weigh him down.

Rubio’s opponents will also seek to attack his credentials, though Cruz welcomed his upper chamber colleague into the race yesterday by noting their similar personal stories. “We’re both the sons of immigrants who escaped Cuba to build a better life in the United States, and we share a deep appreciation and understanding of what it means to work hard and achieve the American Dream,” the Texas senator said in a statement.

Rubio will have to compete with Bush and Walker for money, and a big question surrounding his newly launched campaign is whether he can raise enough cash to sustain himself through at least through the Florida primary.

But Rubio’s tallest challenge at this point is convincing primary voters that his potential to make history as a minority president, along with his soaring rhetoric, appeal to young people, and lack of governing experience don’t mean he is a GOP version of Barack Obama.

Monday’s speech, while obviously different in terms of policy proposals from Obama’s, was reminiscent of that history-in-the-making campaign kickoff.

"It reminds me, I have to say, when Obama announced his [candidacy]. There were a lot of people in the audience there that thought: If you can do it, anybody can," said Patty Miller, the COO of an education company from Philadelphia, who was in Miami on business and came with local friends to hear Rubio speak. "It is the American Dream."