The top two Democrats in Congress suggested Monday that President Trump’s performance during a joint news conference with Russian President Vladi­mir Putin signaled that Russia has damaging information on the U.S. leader.

“President Trump’s weakness in front of Putin was embarrassing, and proves that the Russians have something on the president, personally, financially or politically,” House Minority Leader Nancy Pelosi (D-Calif.) said in a statement. “This is a sad day for America, and for all Western democracies that Putin continues to target.”

Senate Minority Leader Charles E. Schumer (D-N.Y.) was less direct but raised the same prospect in a statement issued shortly after Trump and Putin concluded a remarkable news conference in Helsinki at the end of a summit that both said included discussion of Russian interference in the U.S. 2016 presidential election.

“A single, ominous question now hangs over the White House: What could possibly cause President Trump to put the interests of Russia over those of the United States?” Schumer said in a statement. “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.”

During the news conference, Putin again denied any election interference, and Trump cast doubt on the conclusion of U.S. intelligence agencies to the contrary.

“I don’t see any reason why” Russia would interfere in the election, Trump told reporters, also characterizing the probe by special counsel Robert S. Mueller III as “a disaster for our country.”

Asked whether the Russian government has compromising material on Trump, Putin said he was aware of “rumors” that such material was collected during a 2013 visit by Trump to Moscow but that it was “difficult to imagine” that had occurred.

“When President Trump was at Moscow back then, I didn’t even know that he was in Moscow,” Putin said. “I treat President Trump with utmost respect, but back then when he was a private individual, a businessman, nobody informed me that he was in Moscow.”

Trump’s 2013 visit came in conjunction with the Miss Universe pageant, which he owned. A dossier compiled by a former British spy contains salacious allegations about Trump’s behavior on the trip, which Trump has denied.

At a news conference later Thursday, Schumer elaborated on his statement and called on Republicans to stand up to Trump.

“Where are the Republicans who know in their heart the president is giving away the store to Vladimir Putin?” Schumer said on Capitol Hill. “The best people to check him are not Democrats but his fellow Republicans.”

Schumer called on those in the GOP to do four things: ratchet up sanctions against Russia; end their attacks on the FBI, Justice Department and Mueller; invite Trump’s national security team to testify before Congress about preparations for the summit with Putin; and push the president to call on Putin to extradite the 12 military intelligence officers were indicted last week on charges they hacked Democrats’ computers, stole their data and published those files to disrupt the 2016 election.