House Minority Leader Nancy Pelosi (D-Calif.) and other Democratic lawmakers criticized President Donald Trump following his summit with Russian President Vladimir Putin.

Pelosi tweeted that Trump failed to stand up to Putin during a press conference on Monday when he was asked about Russia's meddling in the 2016 election.

She suggested that the Russians must have something on Trump, arguing that there is no other explanation for his "refusal" to condemn Russia's election interference.

Russian Studies Professor: US-Russia Relations Are 'More Dangerous' Than Ever Before

Hilton: 'A Vintage Week for Unthinking, Anti-Trump Bigotry & Hate'

Senate Minority Leader Chuck Schumer (D-N.Y.) echoed the sentiment, tweeting that Americans have never seen a U.S. president "support an American adversary" the way Trump has supported Putin.

"Millions of Americans will continue to wonder if the only possible explanation for this dangerous behavior is the possibility that President Putin holds damaging information over President Trump," Schumer wrote.

Other Democratic lawmakers also weighed in, with Sen. Bernie Sanders (I-Vt.) calling the Trump-Putin summit an "embarrassing spectacle" and Sen. Elizabeth Warren (D-Mass.) dubbing it "disgraceful."

Democrats weren't the only ones who were critical of Trump's remarks on Russia's election meddling.

Sen. Lindsey Graham (R-S.C.) said it was a "missed opportunity" by Trump to hold Russia accountable and Sen. Ben Sasse (R-Neb.) said Trump should have declared Russia an "enemy of America and our allies."

Meantime, Sen. Jeff Flake (R-Ariz.) said it was "shameful" for Trump to place blame on the U.S. for "Russian aggression."

Watch the "Outnumbered" panel react to the summit and the subsequent criticism in the clip above.

'Own This Debate': Ex-CIA Officer Says Trump Must Enforce a Red Line With Putin

Trump Greets Putin in Helsinki, Predicts US & Russia Will Have 'Extraordinary Relationship'

Terror Expert Compares Reaction to Trump's Russia Efforts to Obama's: ‘It's Glaring Hypocrisy’