Schumer vows votes on background checks, voting rights after break
McCain rips Trump: NATO actions 'disappointing' but not surprising
"There is little use in parsing the president's misstatements and bluster, except to say that they are the words of one man. Americans, and their Congress, still believe in the transatlantic alliance and [NATO], and it is clear that our allies still believe in us as well," McCain said in a statement.
The Arizona Republican, who is absent from Washington as he battles brain cancer, added that Trump's "performance" in Brussels was "disappointing, yet ultimately unsurprising."
Trump sparked disbelief among European allies for his rhetoric at the summit, including his brief war of words with German Chancellor Angela Merkel. Trump said Germany was "captive" to Russia, citing an energy pipeline, and used the summit to repeat calls for allies to increase their defense spending.
Congress took symbolic shots at Trump's rhetoric this week, with the House passing a resolution supporting NATO and the Senate using a procedural vote to signal its support.
Trump traveled to the United Kingdom after the NATO summit on Thursday and is expected to meet next week with Russian President Vladimir Putin in Helsinki.
McCain added that Trump must "reverse his disturbing tendency to show America's adversaries the deference and esteem" that should be reserved for allies. And noting that the world will be watching the one-on-one meeting, he urged Trump to be "strong and tough" against Putin.
"It is up to President Trump to hold Putin accountable for his actions during the meeting in Helsinki. Failure to do so would be a serious indictment of his stewardship of American leadership in the world," he said.