Sen. John McCain calls President Donald Trump's press conference with Russian President Vladimir Putin "one of the most disgraceful performances by an American president in memory."

The Arizona Republican says the summit with Putin in Helsinki was "a tragic mistake."

Today’s press conference in #Helsinki was one of the most disgraceful performances by an American president in memory. My full statement on the #HelsinkiSummit: https://t.co/lApjctZyZl — John McCain (@SenJohnMcCain) July 16, 2018

The senator says Trump proved not only unable, "but unwilling to stand up to Putin." And he said Trump and Putin "seemed to be speaking from the same script" as Trump made a "conscious choice to defend a tyrant."

McCain, who has been away from the Senate as he battles brain cancer, said the damage inflicted by Trump's "naivete, egotism, false equivalence, and sympathy for autocrats is difficult to calculate."