Mr. Rubio, who visited Israel and Jordan last month, is advocating a more muscular brand of global leadership and observers said it is significant that the Florida lawmaker tapped Jamie Fly, an adviser to President George W. Bush, as a counselor on foreign affairs and national security.

“What you are getting from Rand is really what he thinks,” said James Jay Carafano, vice president of defense policies studies at the Heritage Foundation. “What you are getting from Rubio is in part Jamie, who is more senior, more experienced, and who is more on the side of the offensive realists.”…

But Chris Preble, of the libertarian-leaning Cato Institute, said Mr. Rubio inherited the neoconservative approach from Sens. John McCain of Arizona and Lindsey Graham of South Carolina, military hawks who supported the wars in Iraq and Afghanistan, as well as U.S. involvement in Libya and have more recently urged lawmakers to arm Syria’s rebels — a position Mr. Rubio has not taken.