WASHINGTON >> President Donald Trump today warned Sen. John McCain that “I fight back” after McCain questioned “half-baked, spurious nationalism” in America’s foreign policy.

McCain, a former Navy pilot who spent 5-1/2 years in a Vietnam prisoner of war camp and is battling brain cancer, offered a simple response to Trump: “I have faced tougher adversaries.”

Trump said in a radio interview with WMAL in Washington, “I’m being very, very nice, but at some point I fight back and it won’t be pretty.” He bemoaned McCain’s decisive vote this past summer in opposition to a GOP bill to dismantle Barack Obama’s Affordable Care Act, a move that caused the failure of GOP efforts to repeal and replace “Obamacare.”

In Philadelphia on Monday night, the six-term Republican senator from Arizona received an award for a lifetime of service and sacrifice to the country. In addition to recalling his more than two decades of military service and his imprisonment during the war, McCain took a moment to go a step further than the night’s other speakers, who lamented what many described as a fractured political climate.

“To abandon the ideals we have advanced around the globe, to refuse the obligations of international leadership for the sake of some half-baked, spurious nationalism cooked up by people who would rather find scapegoats than solve problems,” he said, “is as unpatriotic as an attachment to any other tired dogma of the past that Americans consigned to the ash heap of history.”

He continued, “We live in a land made of ideals, not blood and soil.”

Former Vice President Joe Biden presented McCain with the Liberty Medal. Though members of opposing parties, the two men worked together during their time in the Senate. Former President Barack Obama, who defeated McCain in his bid for the presidency in 2008, congratulated the senator on the award in a tweet Monday night.

“I’m grateful to SenJohnMcCain for his lifetime of service to our country. Congratulations, John, on receiving this year’s Liberty Medal,” Obama wrote.

Another political foe, 2012 GOP presidential nominee Mitt Romney, said on Twitter, “Ran against him, sometimes disagree, but proud to be a friend of SenJohnMcCain: hero, champion of character and last night, Lincolnesque.”

The back-and-forth between the president and McCain represented the latest skirmish between the two Republican Party heavyweights and another example of Trump tangling with GOP senators who could undermine his agenda in Congress.

Trump in recent weeks has feuded with Tennessee Sen. Bob Corker and Senate Majority Leader Mitch McConnell, although the president joined with the Kentucky senator at the White House to publicly declare they were on the same page. McCain played a consequential role in the health care debate and will be lobbied heavily to support the president’s push to overhaul the tax system.

In the radio interview, Trump aired his frustration with fellow Republicans who have eluded him in his attempt to overhaul the health care law approved during President Barack Obama’s administration.

“We need some votes from some of the Republicans. For some reason they weren’t there on health care. They should have been,” Trump told WMAL’s Chris Plante. “We thought we had it. John McCain voted no, which was a shocker.”

As a presidential candidate, Trump said in 2015 that McCain was “not a war hero” because he was captured in Vietnam, adding, “I like people who weren’t captured.” McCain, the 2008 Republican presidential nominee, said Trump owed other veterans an apology.

During Trump’s presidency, McCain has questioned the president’s immigration policies and warned him against cozying up to Russian President Vladimir Putin. The senator also criticized Trump in August for saying that both white nationalists and counterprotesters were responsible for violent clashes in Charlottesville, Va.

McCain insisted in a tweet that “there’s no moral equivalency between racists & Americans standing up to defy hate and bigotry,” and the president should say so.

The senator underwent surgery in mid-July to remove a 2-inch blood clot in his brain after being diagnosed with an aggressive tumor called a glioblastoma. It’s the same type of tumor that killed Sen. Edward M. Kennedy at age 77 in 2009 and Beau Biden, son of then-Vice President Joe Biden, at 46 in 2015.

Pressed on Trump’s threat this morning, McCain told reporters he has had tougher fights, and then smiled.

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AP congressional correspondent Erica Werner contributed to this report.