The day after the final Republican debate before Super Tuesday, presidential frontrunner Donald Trump unveiled the endorsement of New Jersey Gov. Chris Christie. Meanwhile, Marco Rubio is ramping up his attacks on Trump, labeling the billionaire businessman a "con artist." Voters in 12 states head to the polls on Tuesday, and half the delegates needed for the GOP nomination are up for grabs. Is Trump unstoppable as he marches to his party's nomination? Plus, President Obama finds himself in a high-stakes battle with Senate Republican leaders who refuse to consider anyone to fill the vacant Supreme Court seat or address the president's plan to close the Guantanamo Bay military prison.