Sen. Tim Johnson has been conscious at times since his emergency brain surgery last week, his spokeswoman said Monday. But he is currently being sedated so he can rest.
The South Dakota Democrat has made it through the first 72 hours since the Wednesday evening brain surgery, spokeswoman Julianne Fisher said, a benchmark that doctors consider a good sign for recovery.
The senator remains in critical but stable condition, she added.
Fisher said the next "target" for doctors is to watch his progress over the next week.
The senator showed some signs of recovery late last week, responding to voices, opening his eyes and moving his limbs. But his long-term prognosis is still unclear.
Control of the Senate
Johnson's sudden illness has raised questions about the Democrats' one-vote majority in the upcoming Senate session. South Dakota's Republican governor, Mike Rounds, would appoint a replacement if Johnson's seat were vacated by his death or resignation.
A Republican appointee would create a 50-50 tie and effectively allow the GOP to retain Senate control because of Vice President Dick Cheney's tie-breaking vote.
There is ample precedent for senators to continue to hold office while incapacitated.
Senate Democratic leader Harry Reid said Sunday on ABC's "This Week" that Johnson has shown significant improvement.
"Doctors tell us everything is going to be just fine," Reid said.
Surgeons at the George Washington University Hospital have said Johnson was experiencing post-surgery swelling in his brain, but they said that was normal.
Johnson, 59, has been diagnosed with arteriovenous malformation, a condition that causes arteries and veins to grow abnormally large, become tangled and sometimes burst. The condition often is present from birth.