"The president called this a hoax publicly. Nothing in the briefing that we have just received led me to believe it is a hoax," Hoyer said.
Representative Adam Schiff, chairman of the House Intelligence committee, said the United States should weigh new sanctions on Russia to deter its "malign" actions after the White House briefing.
Democratic members of Congress emerged from the briefing critical of U.S. President Donald Trump, who the New York Times reported had received a written intelligence briefing on the suspected Russian program in February.
The White House has said Trump did not receive a personal briefing on the issue but has yet to squarely address whether he had received a written briefing, whether he had read it, and why he had not responded more aggressively if he had.
Schiff said Trump should not be courting Russian President Vladimir Putin by inviting him to a Group of Seven (G7) summit of leading industrial nations but rather should impose costs on Moscow.
"The president of the United States should not be inviting Russia into the G7 or G8. We should be considering what sanctions are appropriate to further deter Russia's malign activities," he told reporters after the White House briefing.
The White House has sought to play down reports in the Times and the Washington Post that it knew about accusations that Russia paid the Taliban bounties to kill U.S. and other coalition troops but had not briefed Trump or moved on the information.
That raised serious concerns among both Trump's fellow Republicans and Democrats not only about the safety of U.S. forces but also about the administration's handling of the matter.