“It’s just a reminder that in a 50-50 Senate any unexpected development could be a challenge to our moving forward on an agenda that the Democratic caucus shares,” said Sen. Chris Coons (D-Del.), who said he was very optimistic that the 49-year-old Luján would make a full recovery.

Underscoring the narrow majority, Democrats on the Commerce Committee, which Luján is a member of, almost immediately yanked three nominations that were expected to get votes on Wednesday. An aide noted that the agenda was being “recalibrated to take into consideration the need for all Democratic votes in order to move certain nominees forward.”

The announcement appeared to catch senators off guard.

“Oh my god. I didn’t know that,” said Sen. Dick Durbin (D-Ill.), the No. 2 Senate Democrat.