AIR FORCE ACADEMY, Colo. – President Obama implored the next generation of U.S. military leaders Thursday not to give in to isolationism or pull back from U.S. leadership in the world, drawing a contrast with a foreign policy vision that’s been laid out by Donald Trump.

Obama used his final commencement address as president to reassure the military that it remains the dominant fighting force in the world, implicitly pushing back on critiques that the military’s might has ebbed under his watch. Under searing sun and sweeping blue skies at the U.S. Air Force Academy, he told graduates they’d be called upon to strike a complicated balance between realism and idealism, withdrawal and overreach.

“We can’t be isolationists. It’s not possible in this globalized, interconnected world,” Obama said. “In these uncertain times, it’s tempting sometimes to try to pull back and wash our hands from conflicts that seem intractable, let other countries fend of themselves.”

Calling isolationism a “false comfort,” he added that history had shown how “oceans alone cannot protect us.”

Though Obama didn’t mention Trump or any other presidential candidates, his intended target was clear. Trump, the presumptive Republican nominee, has called repeatedly for putting “America first” by rethinking U.S. alliances, spending less to ensure other countries’ security and enacting strict tariffs that Trump acknowledges could potentially lead to a trade war.

Obama’s rebuke of that philosophy came the same day the likely Democratic nominee, Hillary Clinton, was launching a concerted attack against Trump’s foreign policy with a speech in San Diego. Campaign aides said that Clinton planned to assail Trump as dangerous to U.S. national security and unqualified to serve as commander in chief.

UNDERMINING TRUMP’S STANDS

Though Obama has waited to start campaigning in earnest until the Democratic primary is concluded, he’s worked increasingly to undermine Trump’s appeal by attacking his policies both directly and indirectly. A day earlier, Obama was in a conservative stretch of Indiana on a self-described “myth-busting” mission to derail Republican arguments on the economy.

“When we panic, we don’t make good decisions,” Obama told the Air Force Academy graduates and their families. He said that the U.S. had to engage with the world but must also be wary of overextending itself, particularly with regard to military intervention.

“We have to chart a smarter path,” he said. “As we saw in Vietnam and the Iraq war, often times the greatest damage to American credibility comes when we overreach, when we don’t think through the consequences of all of our actions.”

SINGLES OUT VALUE OF NATO

In another clear nod to Trump, Obama specifically mentioned the value of NATO, an alliance that Trump has suggested is outdated.

Of the 812 graduates of the Air Force Academy this year – all of whom were handed diplomas by the president – 345 are going on to train as pilots, the Air Force said. Sixty of them will train to operate remotely piloted aircraft, such as drones, which have become a central tool of U.S. counterterrorism efforts under Obama. About one-quarter of the class is female while 17 of the graduates come from outside the U.S.

For Obama, the speech is the culmination of a yearly tradition of addressing one of the military’s four service academies at graduation. This year, Obama also delivered commencement addresses at Howard University, a historically black school in Washington, and Rutgers University, a public university in New Jersey.