MIAMI -- U.S. Sen. Marco Rubio entered the presidential race Monday with a promise to move the U.S. beyond the politics of the past, a jab at both Democratic favourite Hillary Rodham Clinton and former Florida Gov. Jeb Bush.

Standing in front of a banner that proclaimed "A New American Century," the 43-year-old Cuban-American used his first speech as a presidential candidate to take on two of America's political dynasties. In doing so, the first-term Florida senator who hopes to become the first Hispanic president bet heavily on Americans' frustrations with Washington and his ability to change how Republicans are seen by voters.

"This election is not just about what laws we will pass," he said Monday evening. "It is a generational choice about what kind of country we will be."

He said it's also a choice between the haves and have-nots, nodding to his own upbringing by working-class, immigrant parents.

Rubio faces steep challenges to the nomination, including a well-funded one that Bush is expected to offer. The son of one president and brother of another, Jeb Bush once mentored Rubio.

Rubio spoke first to his top donors a day after Clinton announced her bid for the Democratic nomination. Rubio told his most generous backers that he feels "uniquely qualified" to pitch his party as one that will defend the American Dream, a dream he said was fading for too many families.

Clinton's entrance into the race with an online video Sunday was robbing some attention from Rubio's splash into the race. But Rubio saw an opportunity to cast the presidential contest as one between a fresh face representing a new generation of leadership and familiar faces harking back decades -- namely, the 62-year-old Bush and the 67-year-old Clinton.

Rubio's swipe at Bush was implied; with Clinton, he was more direct.

"Just yesterday, we heard from a leader from yesterday who wants to take us back to yesterday, but I feel that this country has always been about tomorrow," he told donors.

Rubio held his kickoff rally at Freedom Tower, the Miami landmark that was the first stop for tens of thousands of fleeing Cuban exiles during the 1960s and 1970s.

To counter views of him as a neophyte, Rubio has outlined specific policy proposals both on foreign and domestic issues. He plans future presentations as his campaign gets underway.

On Tuesday, on his first full day as a candidate, he is set to return to Washington to join a Senate hearing on a proposed deal with Iran on its nuclear ambitions.

Rubio is the third major Republican contender to declare himself a candidate, after Sen. Ted Cruz of Texas and Sen. Rand Paul of Kentucky, in a field that could grow to 20 or more.

------

Elliott reported from Washington.