Senator Ben Ray Luján, Democrat of New Mexico, suffered a stroke last week and is expected to make a full recovery, his chief of staff said on Tuesday.
Mr. Luján, 49, checked himself into a hospital in Santa Fe, N.M., on Thursday after experiencing dizziness and fatigue, before being transferred to the University of New Mexico Hospital in Albuquerque, said Carlos Sanchez, his chief of staff.
“Senator Luján was found to have suffered a stroke in the cerebellum, affecting his balance,” Mr. Sanchez said in a statement posted to the senator’s Twitter account. “As part of his treatment plan, he subsequently underwent decompressive surgery to ease swelling.”
“He is currently being cared for at U.N.M. hospital, resting comfortably.”
Mr. Luján’s office did not say how long he might be out, but with Senate Democrats’ fragile 50-50 majority, a prolonged absence from a member who caucuses with Democrats is likely to imperil, or at least delay, Democratic legislation or presidential appointments that come to the Senate floor without Republican support.
Several Democrats said on Tuesday that they were relieved that Mr. Luján would recover, but declined to comment on the political implications of Mr. Luján’s stroke, telling reporters they were concerned primarily about his health and were still processing the news.
“It’s hard to evaluate what it means for here,” said Senator Bob Casey, Democrat of Pennsylvania. “On the human level, it’s scary. It just reminds all of us how good health is something we hope to be blessed by.”
Mr. Luján joined the Senate last year, taking the open seat of the retiring Senator Tom Udall after a dozen years in the House, where he had been seen as an eventual potential replacement for Speaker Nancy Pelosi.
In his first year in the Senate, Mr. Luján introduced a version of the Native American Voting Rights Act, a bill that aims to ease barriers to voting access for Native Americans, a key constituency in his state.
At least one Republican expressed hopes that concern for Mr. Luján’s health could avoid any acrimony while the Senate continues its work.
“My hope is that we all love each other enough to just slow down, do work that we can get done that won’t be affected by his being gone and get him the hell back here when it’s safe,” said Senator Kevin Cramer, Republican of North Dakota. He added, “Gosh, just the nicest guy in the world.”
But Mr. Luján’s absence comes at a critical time for Senate Democrats. President Biden has vowed that he will name a Supreme Court successor for Justice Stephen G. Breyer by the end of February. Although Mr. Luján is not a member of the Senate Judiciary Committee, which considers Supreme Court nominations before a full vote in the Senate, a prolonged absence could still derail the nomination process if Republicans are united in opposition to the nominee.
Lawmakers who have fallen ill have jeopardized legislation in the past, particularly in the Senate, where the loss of a single vote can significantly alter the balance of power.
The absence of Senator Edward M. Kennedy, Democrat of Massachusetts, on Capitol Hill as he battled brain cancer in 2009 complicated efforts to pass the Affordable Care Act. Mr. Kennedy died later that year, and was replaced by Scott Brown, a Republican, in a 2010 election, further hindering efforts to pass the legislation.