Senate Majority Leader Mitch McConnell, a Republican, told reporters: "I’ve said a number of times and I’ll say it again. The Russians are not our friends and I entirely believe the assessment of our intelligence community."
Senate Foreign Relations Committee Chairman Bob Corker, a Republican, said Trump's comments next to Putin made the United States look like a "pushover."
Republican Senator Lindsey Graham said the summit was a "missed opportunity by President Trump to firmly hold Russia accountable for 2016 meddling and deliver a strong warning ...This answer by President Trump will be seen by Russia as a sign of weakness and create far more problems than it solves."
Senator Susan Collins said Trump's "position is untenable," while Senate Intelligence Committee Chairman Richard Burr, also a Republican, outlined Russian aggression on several fronts and said the United States "will not tolerate hostile Russian activities against us or our allies."
Senate and House Democratic leaders Schumer and Nancy Pelosi went so far as to hint that Trump's conduct might stem from Putin possibly having embarrassing information about him.
Schumer said Trump's approach in Helsinki was unprecedented.
"For the president of the United States to side with President Putin against American law enforcement, American defense officials, and American intelligence agencies is thoughtless, dangerous, and weak," Schumer said.