Nonetheless, members of both parties said they were reassured by the hour-long administration update, which President Donald Trump appeared at only briefly before handing the session off to his top national security aides.
"It was a sobering briefing, and an important opportunity for the entire Senate to hear the emerging plans of the Trump administration to confront what is a very real threat to our security," said Sen. Chris Coons, a Democrat from Delaware.
Other lawmakers said they learned little during the session, which was held in a large auditorium in a building adjacent to the West Wing.
"It was an OK briefing," said Sen. Bob Corker, the Republican chairman of the Senate Foreign Relations Committee.
Sen. Jeff Merkley, a Oregon Democrat, said on CNN's "Erin Burnett OutFront" that they learned nothing new in terms of details on the administration's thinking on North Korea and any potential actions the US could take in response to another nuclear test. He said he believed the White House's decision to have the meeting was for "optics."
"We learned nothing you couldn't read in the newspaper," Merkley said.
Likewise, Sen. Tammy Duckworth, an Illinois Democrat, said on CNN's "Anderson Cooper 360" that she did not see new information in the White House briefing "at all."
"It felt more like a dog and pony show to me than anything else," Duckworth said. "I guess it has something to with this 100 days in office."
The varied responses came after some grumbling from lawmakers about the highly unusual nature of convening the session on White House grounds instead of on Capitol Hill. Administration officials said it was merely a logistical choice rather than an attempt to convey any particular message.
Secretary of State Rex Tillerson, Director of National Intelligence Dan Coats, Defense Secretary James Mattis and Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, led Wednesday's session.
Lawmakers traveled together in a fleet of buses from across town to attend the hour-long mid-afternoon briefing. Returning to Capitol Hill, none said they heard any new revelations from the administration officials.
"I didn't hear anything new because I have been heavily briefed before," said Sen. John McCain, the chairman of the Senate Armed Services Committee. "It's a very serious situation, just as I had (thought) before I went there."
Expectations for the session had varied among lawmakers, who are usually briefed on national security matters on Capitol Hill.
Some said they looked forward to hearing directly from Trump about his strategy moving forward. Others questioned why the session was occurring at the White House at all, suggesting the gathering could amount to a substance-free -- and inconvenient -- photo-op.
Trump administration officials, however, downplayed any suggestion that holding the meeting on the White House campus was meant to convey any particular message. Instead, they characterized it as a logistical arrangement between Trump and Senate Majority Leader Mitch McConnell.
"That meeting is a Senate meeting led by Leader McConnell, just utilizing our space," White House press secretary Sean Spicer said. "So that is their meeting. So we're not there to talk strategy."
Speaking to reporters, Coons said the decision to brief every US senator sent a positive signal about the administration's seriousness in addressing threats from North Korea.
"I'm fine coming here," he said. "Frankly if the President and his entire national security leadership team wants to provide a thorough, detailed consultation with the Senate, I think that's constructive."
A spokesman for McConnell said Tuesday that Trump himself offered the White House as a venue for the briefing after McConnell requested an administration update on North Korea.
"The President offered to host the meeting and the Majority Leader agreed," said McConnell's spokesman, David Popp.
The auditorium on the White House grounds is not typically used for large-scale national security briefings, but can be outfitted to accommodate classified discussions among the lawmakers and officials, a White House official said.
Senators are regularly briefed by the administration on national security issues, particularly those lawmakers who sit on committees with oversight of intelligence and national security agencies. But typically those briefings occur on Capitol Hill, where rooms are specially designed for that type of sensitive discussion.
Following Wednesday's White House gathering, many of the administration officials who conducted the meeting traveled to Capitol Hill to brief members of the House.
"I, frankly, don't understand why it's not easier to bring four people here than it is to take 100 there," said Sen. Angus King, a Maine independent who caucuses with Democrats, on Capitol Hill Tuesday.
At Tuesday's weekly Democratic caucus lunch, there was "grumbling" about the optics of senators being summoned to the White House, according to a person in the room.
"Is this a real briefing or is this another Trump dog-and-pony show? This feels very much that this is just a Trump request to hold a photo-op, it is totally outside the normal boundaries," said a Democratic congressional aide, who also questioned the security of the White House auditorium.
"A (secure facility) exists (on Capitol Hill) for a reason," the aide said. "Will he be treating this as a stunt, is that the approach that he is bringing the briefing or will this be a serious conversation about North Korea?"
Popp, McConnell's spokesman, downplayed the notion that the setting is unusual and waved off some Democratic concerns over what they see as theatrics playing into the briefing.
"This is just like any other all-senators briefing. Just a different location," Popp said.