John McCain Slams Trump's NATO Performance: 'Putin Is Our Enemy' and Must Be Held 'Accountable'

Arizona Senator John McCain issued a scathing rebuke Thursday of President Donald Trump's performance at the annual NATO summit, calling it "disappointing yet ultimately unsurprising" and urged the president to "hold Putin accountable" during Trump's meeting next week with the Russian president.

"[Vladimir] Putin is not America's friend, nor merely a competitor," McCain said. "Putin is America's enemy, not because we wish it so but because he has chosen to be."

While at the NATO summit, Trump talked about what he might say to Putin at next week's meeting in Helsinki, Finland,

"What am I going to do?" Trump asked at a press conference at the summit's conclusion. "All I can do is say, 'Did you?' and 'Don't do it again.' But he may deny it. You'll be the first to know." He added that Putin was "not my enemy" and that "hopefully, someday, he'll be a friend. It could happen."

McCain listed Putin's annexation of Crimea from Ukraine, his continued support of the Syrian regime of Bashar al-Assad and its brutality against its own people, and Russian interference in the 2016 election as reasons why the Russian president "has chosen to be" America's enemy.

#Putin is not our friend nor merely a competitor. Putin is our enemy—not b/c we wish it so, but b/c he has chosen to be. He chose to invade Ukraine & annex Crimea. He chose to help Assad slaughter Syrians. He chose to attack our election & undermine democracies around the world.

— John McCain (@SenJohnMcCain) July 12, 2018

"It is up to President Trump to hold Putin accountable for his actions during the meeting in Helsinki," McCain said. "Failure to do so would be a serious indictment of his stewardship of American leadership in the world."

The Republican senator has long expressed outspoken criticism of Trump's praise for the Russian leader.

During the summit with NATO leaders at the alliance's headquarters in Brussels, Trump seemed to shock world leaders on multiple occasions.

The president accused Germany of being "totally controlled by Russia," reportedly spent part of a dinner bragging to allies about his unprecedented meeting with North Korea's Kim Jong Un, demanded that NATO double its military spending target, and said he "probably [could]" withdraw the U.S. from NATO without congressional approval, although it's "unnecessary."

"President Trump may have crossed a new red line today in a NATO summit performance so adversarial... current and former officials from both sides of the aisle are sounding alarms ..." - @PeterAlexander pic.twitter.com/dJ2TxQQxw4

— Deadline White House (@DeadlineWH) July 11, 2018

As Trump used Wednesday's breakfast to accuse Germany of being "captive to Russia" and demanded countries pay more for NATO, even the president's chief of staff, John Kelly, who sat a few feet away from Trump at the table, seemed noticeably uncomfortable. White House press secretary Sarah Huckabee Sanders later claimed the displeased look on Kelly's face was because "he was hoping for a full breakfast and they only had pastries and cheese."

WATCH: Trump Chief of Staff John Kelly looked "noticeably perturbed" during Trump's remarks at NATO breakfast.

The White House says he was "displeased" with the breakfast option: pic.twitter.com/q08pvml9x3

— The Beat with Ari Melber on MSNBC 📺 (@TheBeatWithAri) July 11, 2018