(The Washington Post)

Lawmakers expressed shock and concern after learning that President Trump had revealed highly classified information to the Russian foreign minister and ambassador during a meeting in the Oval Office last week, according to current and former U.S. officials.

“Obviously, they are in a downward spiral right now and have got to figure out a way to come to grips with all that’s happening,” Sen. Bob Corker (R-Tenn.), chairman of the Foreign Relations Committee, said of the Trump administration.

“The chaos that is being created by the lack of discipline is creating an environment that I think makes — it creates a worrisome environment,” he said.

Trump’s disclosures jeopardized a critical source of intelligence on the Islamic State, according to the officials. The information Trump relayed, officials said, had been provided by a U.S. partner through an intelligence-sharing arrangement considered so sensitive that details have been withheld from allies and tightly restricted even within the U.S. government.

(Bastien Inzaurralde,Monica Akhtar/The Washington Post)

The news created a sensation as it spread through Washington and up to Capitol Hill on Monday, where senators were returning for evening votes.

“If the report is true, it is very disturbing,” Senate Minority Leader Charles E. Schumer (D-N.Y.) said in a statement. “Revealing classified information at this level is extremely dangerous and puts at risk the lives of Americans and those who gather intelligence for our country. The President owes the intelligence community, the American people, and Congress a full explanation.”

A spokesman for House Speaker Paul D. Ryan (R-Wis.) emphasized the importance of safeguarding sensitive intelligence.

“We have no way to know what was said, but protecting our nation’s secrets is paramount. The speaker hopes for a full explanation of the facts from the administration,” Ryan spokesman Doug Andres said in a statement.

The revelation came at a sensitive time for the president, who less than a week ago cited “this Russia thing with Trump” in explaining why he fired FBI Director James B. Comey, who was leading an investigation into Russia’s interference with the 2016 election. Investigators are already probing possible coordination between Trump’s campaign and the Russian government, and the president has struggled to shake the issue as he tries to advance his legislative agenda.

The news is likely to raise questions on Capitol Hill about Trump’s handling of classified information. It could also increase pressure on investigators looking into Trump’s possible ties to the Kremlin.

And it could pull attention away from Republicans’ policy priorities this week. The Senate GOP is working to hammer out the details of a health-care plan, and the House is returning from a one-week break.

The top Democrat on the Senate Intelligence Committee called the news a “slap in the face to the intel community.”

“Risking sources and methods is inexcusable, particularly with the Russians,” Sen. Mark R. Warner (D-Va.) tweeted around 6 p.m.

Sen. Ron Wyden (D-Ore.), a member of the panel, said the report was of the “gravest possible concern.”

“This kind of disclosure could harm national security by jeopardizing important sources of information needed to disrupt terrorist attacks,” Wyden said in a statement.

In Moscow, a Russian Foreign Minister spokeswoman, Maria Zakharova, posted a statement on Facebook denying that classified information was provided by Trump, calling the reports “yet another fake.” But denials by Moscow were expected to avoid being pressed for further details.

As senators gathered for their first vote of the week, Republicans and Democrats said they were worried about the developing story. The House was not in session Monday evening.

“Pretty terrifying,” said Sen. Richard Blumenthal (D-Conn.). “If true, it is astonishing, appalling and should be investigated. It was astonishing and absolutely surprising. I would never have imagined the chief executive of our great nation would undertake that kind of disclosure.”

Sen. John Thune (S.D.), chairman of the Senate Republican Conference, said, “I would be concerned anytime we’re discussing sensitive subjects with the Russians.” Thune reacted after an initial briefing on the news report and said he had not reviewed details.

Sen. Joe Manchin III (D-W.Va.), a member of the Intelligence Committee, said he’d only heard the basics of the report but called them “very serious.” He noted that fewer than 25 senators are ever given access to the nation’s most sensitive secrets and he learns things he “can’t even talk about with other senators.”

If the reports are true, “it’s very damning, very damaging,” Manchin said, adding that such disclosures “would be extremely dangerous and concerning to all.”

Sen. Christopher A. Coons (D-Del.) said had he just read The Post story and, “if true, that would be genuinely shocking.”

“It’s disturbing if true,” Sen. Angus King (I-Maine) said.

Several senators said they did not know the details of The Post report but called the news troubling nonetheless.

“This is not the appropriate move on his part, and I just think it’s part of a pattern of recklessness that we’ve got to get a handle on,” said Sen. Martin Heinrich (D-N.M.).

Sen. John McCain (R-Ariz.), chairman of the Armed Services Committee, said, “We certainly don’t want any president to leak classified information, but the president does have the right to do that … I think any president needs to be careful.”

About a dozen reporters continued to stake out a bipartisan health-care meeting around 7 p.m., intent on asking questions about Trump. The scene was reminiscent of the prior week, when Capitol Hill was consumed by news of Comey’s firing.

McCain, clearly flustered by reporters pressing for answers, walked off the Senate floor and said he hadn’t read the reports, adding, “I can’t comment on every breaking news story.”

Later, he said: “That’s why it’s classified. They have a reason to classify it, okay? And when they say it’s classified, if it was public knowledge, then it could hurt the national security of the United States. That’s why we classify.” He said the news would be “disturbing” if true.

Senate Majority Leader Mitch McConnell (R-Ky.) was silent as he walked from his office to the Senate floor. Asked how concerned he was about Trump sharing information with Russian officials, he looked straight ahead, offering no reaction.

Sen. John Cornyn (Tex.), the Republican whip and a candidate to replace Comey as FBI director, said he didn’t have “any information about that at all.”

“I’m just not going to answer a hypothetical question,” he told reporters.

Sean Sullivan and Karoun Demirjian contributed to this report.