Congressional visitors continued to come to the hospital and comfort family members as the South Dakota senator's progress was closely watched across Washington. His sudden illness raised questions about the Democrats' one-vote majority in the upcoming Senate session.
Senate Democratic Leader Harry Reid visited Johnson, 59, at George Washington University Hospital again Friday and said he looked "good, fine." Senate Chaplain Barry Black also came by.
Johnson suffered a brain hemorrhage Wednesday that was caused by an uncommon and sometimes fatal condition, and underwent surgery late into the night.
Johnson's office reports that the senator remains in the ICU in critical but stable condition.
"Considering his initial presentation, his progress is encouraging," Dr. Anthony Caputy said, according to a news release issued by Johnson's office. "He is now stabilized and continues to show signs of responsiveness to the medical staff and the family."
Dr. Vivek Deshmukh, who performed the surgery, added in the release that "His most recent CT Scan shows that the pressure has been relieved from his brain and there is no further bleeding. Currently his brain pressures are normal and we will continue to monitor this closely for several days."
He was responding to the voice of his wife, Barbara, and following directions a few hours after the surgery. When she asked him to open his eyes, he did, and then reached out to hold her hand, said Johnson spokeswoman Julianne Fisher.
"They are just very encouraged by the little things right now," Fisher said Friday.
The senator's two sons, Brooks and Brendan, who live out of town, flew in to be with their father. Johnson's daughter Kelsey lives in Washington.
"I can't imagine how important that was for Barbara to be there at a time in which they started to have him come around and that just makes us all feel better," said South Dakota Gov. Mike Rounds, who has been following Johnson's progress from Sioux Falls.
Rounds, a Republican, would be charged with appointing a replacement if Johnson were to leave office.
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.
Rounds said he was praying for Johnson's recovery.
"My first thought was, is my friend Tim Johnson in trouble, and then I thought about his wife and about his family and what must be going through their minds," said Rounds, who declined to talk about what he might do if he had to name a replacement.
The White House also offered hopes and prayers for Johnson.
Press Secretary Tony Snow said the White House has made a number of attempts to contact Barbara Johnson. He said the White House has not been in contact with Rounds.
"This is a time to pray for Tim Johnson's health, and I'll leave it to others to start doing political calculations," Snow said.
Reid, D-Nev., who is to become majority leader when the new Senate convenes Jan. 4, has visited Johnson at the hospital each day, sometimes more than once.
Other senators have stopped by. Senate Republican Leader Bill Frist, R-Tenn., visited Thursday, as did Sen. Byron Dorgan, D-N.D., and former Sen. Tom Daschle, D-S.D. Sen. Jack Reed, D-R.I., was at the hospital Friday.
Johnson was in critical condition but was described as recovering and stable on Thursday. The senator was on "an uncomplicated postoperative course," the U.S. Capitol physician said after visiting him Thursday afternoon.
"He has been appropriately responsive to both word and touch. No further surgical intervention has been required," said the physician, Adm. John Eisold.
Doctors said it was too early to say whether further surgery would be needed later.
CBS News chief Washington correspondent Bob Schieffer said the question now, if Johnson continues to recover, "is when will he be able to come back on the job."
Historically, "senators in both parties have given a lot of leeway to people with illnesses like this," Schieffer said. "When Sen. Biden had surgery in 1988, for example, no one questioned he was going to be off the job for several months. They waited until he was able to come back and he recovered completely. I think you will see something like that. There will be no push to force him to resign or something like that."
Johnson's office said it expected the senator to continue to be hospitalized "until brain swelling goes down and his overall condition improves. As he presented with weakness on his right side, doctors anticipate that physical therapy will be part of recovery."
Democrats are preparing to take control of the Senate with a 51-49 majority when the new Congress convenes in three weeks. Democrats seized control of both the House and Senate from Republicans in the Nov. 7 midterm elections.
The symptoms first surfaced during a telephone conference call with reporters on Wednesday, reports CBS News correspondent Sharyl Attkisson. In the middle of answering a question, Johnson began to falter.
Johnson was rushed to the George Washington University Hospital where he was diagnosed with arteriovenous malformation, or AVM, a condition that causes arteries and veins to grow abnormally large, become tangled and sometimes burst. The condition often is present from birth.
Eisold, the Capitol physician, said doctors stopped bleeding in Johnson's brain and drained the blood that had accumulated there.
Dr. William Bank, who treats AVMs and other neurovascular disorders at Washington Hospital Center, said Johnson may need more surgery.
"It probably is not over," Bank said. "For a complete removal of an AVM, you need to be doing your surgery under ideal circumstances," not when the defect is actively bleeding.
On Thursday afternoon, Johnson underwent an additional procedure to prevent blood clots. The procedure is standard after surgery, said Julianne Fisher, Johnson's spokeswoman.
Senate historian Donald Ritchie said senators serve out their terms unless they resign or die. Senators have remained in the Senate even though illness kept them away from the chamber for long periods.
Arteriovenous malformation is believed to affect about 300,000 Americans, according to the National Institute of Neurological Disorders and Stroke. The institute's Web site said only about 12 percent of those have any symptoms.
It's common to take several days to wake up after AVM surgery, said Dr. Sean Grady, neurosurgery chairman at the Hospital of the University of Pennsylvania. Someone who is awake and talking in the first day or two typically has a shorter recovery — in the range of four weeks to eight weeks, he said.