Marco Rubio

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Republican presidential candidates, Sen. Marco Rubio, R-Fla., left, Donald Trump, Sen. Ted Cruz, R-Texas, and Ohio Gov. John Kasich, right, stand together before the start of the Republican presidential debate sponsored by CNN, Salem Media Group and the Washington Times at the University of Miami, Thursday, March 10, 2016, in Coral Gables, Fla. (AP Photo/Wilfredo Lee)

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Republican presidential candidate Marco Rubio is pinning his political future on his home state of Florida and its 99 delegates up for grabs Tuesday. Although he is gaining ground on Donald Trump, he is 8 percentage points behind in the pivotal central part of the state. (Associated Press)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla. speaks during a campaign stop, Monday, Feb. 29, 2016, in Knoxville, Tenn. (AP Photo/Wade Payne)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., speaks to the media before he speaks to a crowd at Mount Paran Christian School, Saturday, Feb. 27, 2016, in Kennesaw, Ga. (AP Photo/Mike Stewart)

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Sen. Marco Rubio will speak at 11:35 a.m. Saturday during the March 2-5 gathering of the Conservative Political Action Conference at National Harbor just outside Washington, D.C. (Associated Press)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., speaks at a rally Sunday, Feb. 21, 2016, in North Las Vegas, Nev. (AP Photo/Jae C. Hong)

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Sen. Marco Rubio placed third in Iowa and struggled to a fifth-place showing in New Hampshire. With South Carolina's primary Saturday, Mr. Rubio is trying to overcome nagging immigration questions once again. (Associated Press)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., right, speaks with Republican presidential candidate, businessman Donald Trump during the CBS News Republican presidential debate at the Peace Center, Saturday, Feb. 13, 2016, in Greenville, S.C. (AP Photo/John Bazemore)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., right, hands Republican presidential candidate, businessman Donald Trump a tic tac container at a break during the CBS News Republican presidential debate at the Peace Center, Saturday, Feb. 13, 2016, in Greenville, S.C. (AP Photo/John Bazemore) ** FILE **

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Republican presidential candidate, businessman Donald Trump speaks about Republican presidential candidate, Sen. Ted Cruz, R-Texas, left, as Republican presidential candidate, Sen. Marco Rubio, R-Fla., right, during the CBS News Republican presidential debate at the Peace Center, Saturday, Feb. 13, 2016, in Greenville, S.C. (AP Photo/John Bazemore)

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Republican presidential candidates, from left, Ohio Gov. John Kasich, former Florida Gov. Jeb Bush, Sen. Ted Cruz, R-Texas, businessman Donald Trump, Sen. Marco Rubio, R-Fla., retired neurosurgeon Ben Carson take the stage before the CBS News Republican presidential debate at the Peace Center, Saturday, Feb. 13, 2016, in Greenville, S.C. (AP Photo/John Bazemore) ** FILE **

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Republican presidential candidate Sen. Marco Rubio, R-Fla., speaks during a rally at Greenville Downtown Airport, Friday, Feb. 12, 2016, in Greenville, S.C. (AP Photo/John Bazemore)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla. speaks during a Faith and Family Presidential Forum at Bob Jones University, Friday, Feb. 12, 2016, in Greenville, S.C. (AP Photo/Paul Sancya)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., answers a question during a Republican presidential primary debate hosted by ABC News at the St. Anselm College Saturday, Feb. 6, 2016, in Manchester, N.H. (AP Photo/David Goldman)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., answers a question as Republican presidential candidate, businessman Donald Trump listens during a Republican presidential primary debate hosted by ABC News at the St. Anselm College Saturday, Feb. 6, 2016, in Manchester, N.H. (AP Photo/David Goldman)

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Republican presidential candidate, former Florida Gov. Jeb Bush and Republican presidential candidate, businessman Donald Trump spar as Republican presidential candidate, Sen. Marco Rubio, R-Fla., listens in the middle during a Republican presidential primary debate hosted by ABC News at the St. Anselm College Saturday, Feb. 6, 2016, in Manchester, N.H. (AP Photo/David Goldman)

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Republican presidential candidate, Sen. Marco Rubio, R-Fla., Republican presidential candidate, businessman Donald Trump and Republican presidential candidate, Sen. Ted Cruz, R-Texas, from left, participate during the Fox Business Network Republican presidential debate at the North Charleston Coliseum, Thursday, Jan. 14, 2016, in North Charleston, S.C. (AP Photo/Rainier Ehrhardt) ** FILE **

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Republican presidential candidates, from left, Ohio Gov. John Kasich, New Jersey Gov. Chris Christie, Sen. Marco Rubio, R-Fla., businessman Donald Trump, Sen. Ted Cruz, R-Texas, retired neurosurgeon Ben Carson and former Florida Gov. Jeb Bush participate during the Fox Business Network Republican presidential debate at the North Charleston Coliseum, Thursday, Jan. 14, 2016, in North Charleston, S.C. (AP Photo/Chuck Burton) ** FILE **

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Republican presidential candidates, from left, Ohio Gov. John Kasich, New Jersey Gov. Chris Christie, Sen. Marco Rubio, R-Fla., businessman Donald Trump, Sen. Ted Cruz, R-Texas, retired neurosurgeon Ben Carson and former Florida Gov. Jeb Bush take the stage before the Fox Business Network Republican presidential debate at the North Charleston Coliseum, Thursday, Jan. 14, 2016, in North Charleston, S.C. (AP Photo/Rainier Ehrhardt)