Today: Jake Tapper spoke exclusively with Republican presidential candidate Sen. Marco Rubio about Donald Trump, the Iran deal, immigration, Cuba, and much more. As President Obama battles to defend the Iran deal, Secy. of State John Kerry and Secy. of Energy Ernest Moniz insist there is no alternative. And, Gov. Scott Walker spoke exclusively with Dana Bash inside his RV as he toured Iowa. He spoke on Iran, his Boy Scouts comments, and much more.