President Donald Trump signed a defense bill named after Sen. John McCain of Arizona during a ceremony at Fort Drum, New York, on Monday.

Trump thanked several lawmakers during his speech, but he did not mention McCain, a former US Navy pilot and a prisoner-of-war.

CNN host Jake Tapper thanked McCain in place of the president.

The feud between Trump and McCain has escalated, particularly after the senator became an outspoken critic for many of Trump's policies.

CNN host Jake Tapper thanked Sen. John McCain of Arizona for his lifelong service to the country after President Donald Trump signed the John S. McCain National Defense Authorization Act without mentioning McCain's service.

Trump thanked several lawmakers during his speech in front of dozens of US service members at Fort Drum, New York on Monday, but did not mention McCain, a former US Navy pilot, prisoner-of-war, and one of the longest serving US senators.

"We would not be here for today's signing ceremony without the dedicated efforts without the dedicated members of Congress who worked so hard to pass the National Defense Authorization Act," Trump said as he thanked several lawmakers, including Rep. Martha McSally of Arizona and Rep. Elise Stefanik of New York.

President Donald Trump during his speech to US service members at Fort Drum, New York, August 13, 2018. Carolyn Kaster/AP

The absence of any mention of McCain — whom the defense bill is named after — raised eyebrows. Vice President Mike Pence also did not mention McCain.

The Arizona Republican senator has been an outspoken critic of Trump's legislative policies and famously cast a decisive "no" vote on the GOP's repeal of the Affordable Care Act in July 2017, angering Trump.

Tapper took a moment on his program Monday to give the senator his due.

"President Trump just a few minutes ago thanking a laundry list of people before officially signing," Tapper said on CNN. "One person who wasn't on that list of people that he thanked ... You know, the decorated war hero who was a prisoner of war, continues to serve as United States senator, chairman of the [Senate] Armed Services Committee.

"And since President Trump would not do it, let us here on 'The Lead' congratulate Sen. John McCain and his family and thank him for his service to the country," Tapper added.

Sen. Jeff Flake of Arizona, who has not shied from signaling his opposition to Trump, also thanked McCain for his service and said he was "grateful" for McCain's "enduring commitment to our national defense."

Trump has downplayed McCain's military service and said the former Naval aviator was "not a war hero."

"He is a war hero because he was captured," Trump said in 2015. "I like people that weren't captured, OK? I hate to tell you."

The president has continued to throw subtle jabs at the senator after he voiced his opposition on matters of national security, healthcare, and immigration.

Meanwhile, McCain said he was "humbled" and thanked his colleagues for naming the bill after him.

"Serving as Chairman of the Senate Armed Services Committee and working on behalf of America's brave service members has been one of the greatest honors of my life," he said in a statement. "I'm proud that throughout my tenure, the committee has led with a spirit of comity and cooperation to provide for America's Armed Forces."

"There is no higher calling than to serve a cause greater than self-interest," McCain added. "... I've been privileged to support our men and women in uniform who have dedicated their lives to that noble cause.”