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If Marco聽Rubio聽launches his presidential campaign as expected Monday, the first-term Republican senator from Florida may have to answer this simple question. Why now?

The 43-year-old聽Rubio, a rising star on Capitol Hill, could wait four more years, even eight, and still be a relatively young candidate.

Some party officials want him to run for governor or try to hold his Senate seat, which could be crucial to continued Republican control of the chamber. By training his sights on the White House,聽Rubio聽also sets up a head-to-head competition with Jeb Bush, a mentor with whom he has many overlapping supporters.

Rubio聽was expected to announce his candidacy Monday in his hometown of Miami, which would put him in the shadow of Democrat Hillary Rodham Clinton's highly anticipated announcement Sunday of a second White House run in a bid to become the first female U.S. president.聽Rubio, a Cuban-American, could make history too by being the first Hispanic president.

The window to run for president can close as quickly as it opens.

Then-Sen. Barack Obama of Illinois seized an opportunity in 2008 and won. Donors clamored for New Jersey Gov. Chris Christie to run in 2012, but he declined and now heads into the 2016 campaign in a decidedly weaker position.

"There's no telling that (Rubio's) opportunity will be better four or eight years from now," said Fergus Cullen, the former New Hampshire Republican chairman who is yet to throw his support behind a candidate.

Rubio's聽advisers know all about the fickle preferences of the electorate.聽Rubio聽was a beneficiary of the 2010 tea party wave that swept dozens of conservative lawmakers into Congress just two years after Obama and Democrats won big.

But聽Rubio's聽team sees an opportunity to answer the "why now" question and argue the country's pressing problems require a new generation of leaders, not a return to the 1990s.

Rubio聽is about to step into a field that is shaping up to be crowded and competitive.

He won't be the only senator in the race.

He won't be the only candidate seeking support from the ultraconservative tea party movement which advocates smaller government and lower taxes.

He won't even be the only Floridian, the only Cuban-American or the only candidate claiming foreign policy expertise. Texas Sen. Ted Cruz, who is also Cuban-American, is already in the race.

Some are better known 鈥� Bush, for one.

But it is early, and聽Rubio's聽advisers say they are playing a long game. "Campaigns are won at the end, not at the beginning," said Alex Conant,Rubio's聽spokesman.

Miami's Freedom Tower was picked as the expected backdrop for聽Rubio's聽campaign announcement. The landmark was once the federal processing center for tens of thousands of Cuban exiles arriving in the U.S. in the 1960s and 1970s.

Rubio's聽parents left Cuba in 1956, shortly before Fidel Castro took power.

The senator plans to make his family's immigrant past and his own success story a central part of his campaign. He also intends to play up his hawkish foreign policy views and experience on two powerful national security-focused Senate committees as he tries to sell his qualifications to be commander in chief.

Rubio聽was expected to return to Washington in time for a Senate Foreign Relations Committee hearing Tuesday on Iran. Like his Republican presidential rivals,聽Rubio聽has been sharply critical of Obama's deal-making with Iran over its disputed nuclear program.

Rubio聽will headline fundraisers in New York and Boston later in the coming week. He was a strong fundraiser for Republicans in the 2014 elections and a popular draw in their campaigns, though he will be competing with Bush for some high-dollar Florida donors.聽Rubio聽supporters recently announced the formation of a super PAC to bolster his candidacy.

Rubio聽is set to make his first campaign stop as a presidential candidate Friday in New Hampshire, which every four years holds the first presidential primary. He's also expected to visit the other early-voting states 鈥� Iowa, South Carolina and possibly Nevada by the end of the month, aides said.

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