In a speech on Monday in New Hampshire, Rubio blasted the foreign policy failures of "isolationist" Republicans and the Obama administration.
"We have Republican candidates who propose that rulers like Assad and Putin should be partners of the United States, and who have voted with Barack Obama and Harry Reid rather than with our men and women in uniform," Rubio said.
Attacking the Obama administration, Rubio called former Secretary of State Hillary Clinton a "liar," and accused her of "lying to our faces" about the cause of the Benghazi attacks. Rubio promised, "If I am our nominee, voters will be reminded of it time and time again."
Continuing a line of attack he has used against GOP rivals Ted Cruz and Rand Paul, who have to varying degrees embraced a non-interventionist foreign policy, Rubio said, "We have isolationist candidates who are apparently more passionate about weakening our military and intelligence capabilities than about destroying our enemies. They talk tough, and yet they would strip us of the ability to keep our people safe."
Rubio also seemed to take direct aim at his Senate colleague Cruz, who has surged in recent polls and whose political identity was built on anti-establishment spectacles like his controversial filibusters.
"Words and political stunts cannot ensure our security," Rubio warned. "ISIS cannot be filibustered."
Rubio made a not-so-subtle dig at GOP front-runner Donald Trump as well, when he said of the presidency, "The job is not described in the Constitution as 'entertainer in chief,' or 'commentator in chief,' or even, frankly, 'economist in chief.' It is described as Commander in Chief."
He added, "If you can't be bothered to offer specifics on how you will perform that job, then you don't deserve that job."
Trump has publicly avoided discussing the specifics on his national security policies, aside from his call for construction of a wall on the U.S. border with Mexico and his vow to "cut the head off ISIS and take their oil."
But Rubio was at his most animated when denouncing the foreign policy failures of the Obama administration. He ripped Obama for being "willing to abandon our allies, make concession to our enemies, and to make historic, devastating cuts to our military and intelligence capabilities."
"Barack Obama has deliberately weakened America," Rubio charged.
Echoing a theme of renewed American confidence that Rubio's team has sought to make a campaign refrain, Rubio declared, "I will be a President who doesn't just believe America is the greatest country in the world; I will be a president who acts like it."