"The damage inflicted by President Trump's naiveté, egotism, false equivalence, and sympathy for autocrats is difficult to calculate. But it is clear that the summit in Helsinki was a tragic mistake," McCain said in a statement.
The statement about the Putin meeting is just the latest in a string of criticisms the Republican senator has had for Trump during the president's tenure, and McCain touched on the personal traits of Trump's that were exposed in the meeting with Putin.
"President Trump proved not only unable, but unwilling to stand up to Putin," McCain said in the statement. "He and Putin seemed to be speaking from the same script as the president made a conscious choice to defend a tyrant against the fair questions of a free press, and to grant Putin an uncontested platform to spew propaganda and lies to the world."
McCain has a history of spats not only with Trump but also with Russia, as the Arizona senator was sanctioned by Putin in 2015. At the time, McCain said that he "couldn't be more proud" of the sanction, which came amid Russia's efforts to annex Crimea.
In his latest statement, McCain warned of how the meeting with Trump will be seen as an inherent approval of the Putin regime.
"It is tempting to describe the press conference as a pathetic rout -- as an illustration of the perils of under-preparation and inexperience. But these were not the errant tweets of a novice politician," he said. "These were the deliberate choices of a president who seems determined to realize his delusions of a warm relationship with Putin's regime without any regard for the true nature of his rule, his violent disregard for the sovereignty of his neighbors, his complicity in the slaughter of the Syrian people, his violation of international treaties, and his assault on democratic institutions throughout the world."
McCain also took issue with the contrast between the praise that Trump had for Putin compared with the "bombastic and erratic conduct towards our closest friends and allies in Brussels and Britain."
"No prior president has ever abased himself more abjectly before a tyrant," McCain said. "Not only did President Trump fail to speak the truth about an adversary; but speaking for America to the world, our president failed to defend all that makes us who we are —- a republic of free people dedicated to the cause of liberty at home and abroad. American presidents must be the champions of that cause if it is to succeed. Americans are waiting and hoping for President Trump to embrace that sacred responsibility. One can only hope they are not waiting totally in vain."
The senator's daughter, Meghan McCain, a co-host of ABC's "The View" and a regular Republican political commentator, wrote on Twitter that she was "horrified" by the news conference and reiterated her pride in her father's sanction.
"I don’t have anything quippy to tweet. I’m horrified - and have never been more proud of the fact that Putin hates my father so much he personally sanctioned him on Russia's enemies list," she wrote.