"If someone decides to run for president of the United States, you run for president of the United States," Rubio said at the National Press Club. "I don't believe you can run effectively for an office of that magnitude while having some exit strategy in mind."
Lest there be any doubt that he had another contender in mind, Rubio continued, though he didn't mention Paul by name.
"So, others may disagree and may choose a different route. That's my feelings on it," he said. "If someone decides to run for an office of that importance, you do so because that's what you want to be, and you're not trying to find some sort of eject button that allows you to get out if it isn't going well and keep yourself involved in politics."
Paul and Rubio both won their seats in the 2010 election, so they're both up for reelection in 2016. State laws in Kentucky and Florida currently prevent them from running for the two offices at the same time, but Paul is working to have the Kentucky law changed.