Sen. Marco Rubio (R-Fla.) disavowed himself again on Friday from an immigration overhaul plan he once cosponsored, arguing that it didn't work amid lax enforcement by the Obama administration.

Rubio, who cosponsored a bipartisan immigration reform bill in 2013, said he's still eager to deal with the fate of roughly 12 million undocumented immigrants in the country, but "What I’ve learned, is you can’t even have a conversation about that until people believe and know – not just believe, but it’s proven to them – that future illegal immigration will be controlled. That is the single-biggest lesson of the last two years. "

Since the bipartisan bill failed to advance in the GOP-controlled House, Rubio has endorsed a piecemeal approach to solving the nation's immigration issues that begins by fortifying the U.S.-Mexico border before dealing with issues related to legal and illegal immigration. But reiterating those points Friday in front of a room packed with conservative activists helped endear him to the crowd even more.

The first-term senator was greeted with a standing ovation and earned a spirited response from the crowd as he delivered a robust conservative defense of American exceptionalism by jabbing President Obama's foreign policy, subtly digging former secretary of state, Hillary Rodham Clinton, and drawing subtle contrasts between himself and potential GOP rivals for the White House.

Sen. Marco Rubio (R-Fla.) urged the audience at the second day of the 2015 Conservative Political Action Conference to consider what must be done to ensure America remains "exceptional." (AP)

"Sometimes you wouldn’t know we’re an exceptional nation by listening to the president, who’s described our nation as sometimes being arrogant or dictating terms to others," Rubio said. "But Americans know we’re exceptional and you know who else knows we’re exceptional? The world does. After all, when was the last time you heard about a boatload of Americans arriving on the shores of another country?"

"Because of the Obama/Clinton foreign policy, our allies no longer trust us and our enemies no longer fear us," he added later. He said that Obama is running "A foreign policy that treats the Ayatollah of Iran than the prime minister of Israel."

"Imagine if we had a president who doesn’t travel the world bad-mouthing America. After all, that’s the UN’s job," he quipped later.

Rubio was initially expected to speak later in the day, but was given an early-morning slot -- one that will allow him to return to Capitol Hill for votes expected later today as Congress tries to sort out how to avoid a partial shutdown of the Department of Homeland Security

Under questioning by conservative commentator Sean Hannity, Rubio faulted Democrats for holding up consideration of legislation that would block executive actions taken by Obama in November to overhaul the nation's immigration policy. He agreed with Hannity that if Congress ever proceeds on the issue, border security will have to be considered first -- and that changes will need to be fully implemented before the debate can continue.

"The only way forward is you can’t just tell people we’re going to secure the border. … They have to see it they have to see it working and then they’ll have a reasonable conversation with you about the other fronts," he said.

Asked about his presidential aspirations, Rubio wouldn't budge, saying he hasn't made a final decision. But he said he would not run concurrently for president and for reelection to his Senate seat.