Republican presidential candidates, retired neurosurgeon Ben Carson, left, Sen. Marco Rubio, R-Fla., businessman Donald Trump, Sen. Ted Cruz, R-Texas, and Ohio Gov. John Kasich listen to the U.S. national anthem before a Republican presidential primary debate at The University of Houston, Feb. 25, 2016, in Houston. The GOP nominee will need 1,237 delegates at the Republican convention.
Republican presidential candidates, retired neurosurgeon Ben Carson, left, Sen. Marco Rubio, R-Fla., businessman Donald Trump, Sen. Ted Cruz, R-Texas, and Ohio Gov. John Kasich listen to the U.S. national anthem before a Republican presidential primary debate at The University of Houston, Feb. 25, 2016, in Houston. The GOP nominee will need 1,237 delegates at the Republican convention. DAVID J. PHILLIP Associated Press
Republican presidential candidates, retired neurosurgeon Ben Carson, left, Sen. Marco Rubio, R-Fla., businessman Donald Trump, Sen. Ted Cruz, R-Texas, and Ohio Gov. John Kasich listen to the U.S. national anthem before a Republican presidential primary debate at The University of Houston, Feb. 25, 2016, in Houston. The GOP nominee will need 1,237 delegates at the Republican convention. DAVID J. PHILLIP Associated Press

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