By JOHN T. BENNETT, NIELS LESNIEWSKI and JOE WILLIAMSCQ Roll Call

Some senators expressed shock — while others reacted cautiously  — to a report Monday evening alleging that President Donald Trump revealed highly classified information about Islamic State plots gleaned by a U.S. ally to senior Russian officials. 

The Washington Post reported that Trump appeared to be boasting about receiving “great intel” when he allegedly made the disclosure in the Oval Office last week, which the ally had not cleared American officials to share. The White House, however, is denying that he did.

“Obviously, if the allegations are true, that would be very, very troubling,” said Senate Foreign Relations Chairman Bob Corker. “To compromise a source is something that you just don’t do, and that’s why we keep the information that we get from intelligence sources so close as to prevent that from happening.”

Other senators were more measured, however.

“We just have an initial report, so it’s very difficult to comment until we get all facts. I’m not going jump to any conclusion until we get all the facts, as much as I trust The Washington Post,” Senate Armed Services Chairman John McCain said.

Fellow national security hawk Sen. Lindsey Graham is also waiting for further information.

“I don’t know if it’s accurate or not. If it’s accurate, it’d be troubling,” the South Carolina Republican said.

Sen. Jim Risch, an Idaho Republican who serves on the Intelligence Committee, told reporters he was not yet aware of the report as he headed to Monday evening’s floor votes. The same was true of Sen. Bob Casey, D-Pa. (Casey later retweeted a post by Speaker Paul D. Ryan from last year, in which the Wisconsin Republican said “Individuals who are ‘extremely careless’ with classified information should be denied further access to such info.”)

But Sen. Chris Coons had read the Post story.

“That’s really shocking, and there’s obviously going to be a lot more work for us this week,” the Delaware Democrat said. “It’s a reminder that the president, I think somewhat recklessly, chose to welcome the foreign minister of Russia and the ambassador [from] Russia into an Oval Office meeting with reporters who apparently hadn’t been cleared for that.

“The suggestion that he might have shared highly classified information inappropriately with the Russian foreign minister is deeply troubling,” Coons said.

Sen. Mark Warner, the top Democrat on the Intelligence Committee, tweeted a link to the Post story along with his initial reaction.

“If true, this is a slap in the face to the intel community. Risking sources & methods is inexcusable, particularly with the Russians,” he wrote.

Sen. Dianne Feinstein, a former Intelligence Committee chairwoman, told reporters she has a lot of questions to ask. But she also appeared to give Trump the benefit of the doubt — at least for now.

“It does take a period of time to understand it and it’s awful easy to slip,” the California Democrat said when asked whether she believes Trump has a solid grasp of what information is deemed classified.

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Senate Foreign Relations member Christopher S. Murphy, a leading critic of Trump, called it “another very disturbing trend of careless behavior by this administration.”

The Connecticut Democrat also called on GOP lawmakers to step up efforts to investigate possible Trump-Russia ties.

“I don’t know when it will be enough for Republicans to understand that we need to get to the bottom of the connection between the president … and the Russian government,” he said. “But if this story is true, it’s another brick in the wall of a really, really troubling connection between Trump and the Russian government.”

Any sitting U.S. president has the authority to declassify any information he or she sees fit, making it unlikely that Trump broke the law if he did indeed tell Russia’s foreign minister and ambassador to Washington about an ISIS plot involving laptop computers and airliners, as the Post article reported.

A senior White House official denied that Trump disclosed highly classified information during those Oval Office meeting last week.

‘This story is false’

“This story is false. The president only discussed the common threats that both countries faced,” Dina Powell, deputy national security adviser for strategy, who also attended the Oval Office meeting with the Russian officials, said in a statement.

Lt. Gen. H.R. McMaster, Trump’s national security adviser, appeared at the press microphones outside the West Wing at about 7 p.m. Monday and said the Post article “as it came out tonight, is false.”

“The president and the foreign minister reviewed common threats from terrorist organizations to include threats to aviation,” McMaster said. “At no time were any intelligence sources or methods discussed and no military operations were disclosed that were not already known publicly.”

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McMaster said no intelligence sources or methods were discussed during that meeting, adding, “I was in the room, it didn’t happen.”

Notably, the Post report does not allege that those things were discussed in the meeting. It cited multiple current and former U.S. officials.

House Minority Leader Nancy Pelosi said during a CNN town hall Monday night that she was not assured by McMaster’s denial of the Post story.

“The president could be saying something that’s in the public domain but confirming it to the Russians in a way that is very dangerous,” the California Democrat said.

Pelosi described Trump as having a “messy approach to intelligence that is very endangering,” saying, “We cannot have the president of the United States being casually loose-lipped about confirming something — even if it’s in the public domain — to an adversarial nation.”

The report, despite the White House denial, is just the latest Russia-related matter Trump and his team — and, by extension, Hill Republicans — must deal with as they prepare for a major overseas diplomatic trip and try to keep the domestic agenda on track.

For instance, the FBI and multiple congressional panels are investigating Russia’s alleged 2016 presidential election meddling, including possible ties between Trump associates and Russian agents.

Moreover, this latest episode could open Trump to further criticism based on his previous comments about Hillary Clinton. On numerous occasions on the campaign trail last year, Trump criticized his Democratic opponent for her purported mishandling of classified information as secretary of State. He encouraged campaign rally audiences to chant “lock her up” over her use of a private email server during her State Department tenure.

Lindsey McPherson contributed to this report.