South Dakota Sen. Tim Johnson remained in critical condition after undergoing emergency surgery for bleeding in his brain -- an illness that could have immense political implications.
In a statement released by Sen. Johnson's office, Johnson's medical team said they considered the surgery a success.
"Considering his initial presentation, his progress is encouraging. He is now stabilized and continues to show signs of responsiveness to the medical staff and the family" said Dr. Anthony Caputy, chairman of the hospital's Department of Neurosurgery.
Former Democratic Majority Leader Tom Daschle (D-SD) visited Johnson in the intensive care unit Friday afternoon and told reporters upon leaving the hospital, "Another good day -- we're encouraged by the progress."
Earlier in the day Sen. Thomas Carper (D-Del) visited with Johnson's family and described the recovering senator's condition as "a serious situation that's going to be serious for a while" but that signs were "encouraging.
Incoming Majority Leader Sen. Harry Reid (D-Nev), who has visited Johnson at the hospital each day, told reporters Friday morning that Johnson looked good but declined further comment.
The latest news appears to be reassuring for the senator and his family. On Thursday evening, Admiral John Eisold, the Congressional physician, issued a statement saying that Johnson "continue(s) to have an uncomplicated post-operative course. Specifically, he has been appropriately responsive to both word and touch. No further surgical intervention has been required."
Doctors say Johnson, 59, first began experiencing symptoms Wednesday afternoon during a conference call with reporters when he began slurring his speech, stammering, and searching for words.
They say that he has a congenital arteriovenous malformation -- an abnormally tangled network of arteries and veins in his brain that ruptured, causing the bleeding.
From roughly 8 p.m. Wednesday until about 2 a.m. today, Johnson underwent emergency surgery at George Washington University Hospital to stop the bleeding and remove the excess blood.
Johnson's wife Barbara issued a statement today and said their family is "encouraged and optimistic" about his condition. Congressional leaders have echoed those sentiments.
"We're hoping for the best for him and praying for a speedy recovery," said House Speaker-designate Nancy Pelosi, D-Calif.
Republicans universally issued public statements that didn't touch on political concerns but simply prayed for Johnson's recovery.
These came from as far away as Baghdad, where Johnson's 2002 GOP opponent -- Sen. John Thune, R-S.D., who was elected to the Senate two years later -- said he didn't "want to start talking about the what if's."
Thune added that South Dakotans "are hoping and praying for Sen. Johnson for the best possible outcome … We're praying and giving our best possible thoughts to him and his family."
Johnson beat Thune by a reed-thin margin in 2002. His victory in 1996 was also by a slim margin. He is a modest, quiet man in an institution full of egos and sharp elbows, and has a mostly liberal voting record and a moderate demeanor.
His legislative focus is on issues important to his home state of South Dakota -- cattle ranchers, farmers and Native Americans.
But Johnson may be best known for his son Brooks, an Army sergeant who has served in Afghanistan and Iraq, wars Johnson voted for. Before voting to authorize the use of force in Iraq, Johnson said that his son "gives me special empathy for the families of other American servicemen and women whose own sons and daughters may possibly also be sent to Iraq."
Democrats' Majority Challenged?
Beyond praying for a friend, Democrats may also be praying to keep their narrow 51-49 Senate majority.
If Johnson's Senate seat were to become vacant, South Dakota law would empower Republican Gov. Mike Rounds to appoint a replacement.
He would likely pick a fellow Republican, creating a 50-50 Senate with Vice President Cheney as the tie-breaker, leaving the GOP again in control of the Senate.
"By one person changing, the entire Senate changes, changes the president's agenda, changes the Senate's agenda," American University professor James Thurber said. "And that will change events for Iraq, taxes, energy."
Dismissing such talk as premature, Reid said yesterday that everything is still proceeding for his party to assume power.
"There isn't a thing that's changed. The Republicans selected their committees yesterday. We've completed ours," he said.
But Reid, who was with Johnson's family at the hospital Wednesday night and Thursday morning would not say whether Johnson is yet conscious.
"I'm not going to talk about his medical condition. I saw him -- he looked great," Reid said.
Members of the Senate Republican leadership have signaled they will not make an issue of Johnson's potentially prolonged absence from the Senate.
"Johnson can take all the time he needs," said one senior GOP aide. "He's family."
Another senior GOP leadership aide said the position of Senate Republicans is "status quo ante … We're doing the same things today we were doing last week. Nothing's changed."
Historically, senators have remained in office even if an ailment kept them bed-ridden for years. There is no Constitutional requirement for senators to show up to work, Senate historian Richard Baker said. "All that's required is age, residency and citizenship."
Questions about senators not serving their constituents would face the even tougher Constitutional challenge of "Who would decide when a senator was not performing?" Baker said.
"Who would determine whether they are cognizant?" he said. "Do we have a board of doctors that comes in? Is it Terri Schiavo all over again? The framers of the Constitution didn't go there."
Someone making that decision would "remove the sovereignty of the Senate and the independence of Senators," Baker said.
In 1943, the 85-year-old and ailing Sen. Carter Glass, D-Va., stopped coming to work.
As Time magazine reported at the time, the "Senate's cantankerous grand old man was too ill to go to Washington to take what may be his last oath. The Senate adopted a rare resolution and went out to him" at his Lynchburg, Va., home. Colonel Edwin A. Halsey, the Senate Secretary, administered the oath to Glass, who never showed up to work again and died three years later.
In November 1969, Sen. Karl Mundt, R-S.D., was stricken by a severe stroke but he served out the remainder of his term -- staying in office through January 1973. Mundt was stripped of his committee assignments but he remained in office, though "his responsibilities were shouldered by members of his staff," according to the Mundt Archives at Dakota State University.
More recently, in 1988, surgery for a brain aneurism kept Delaware Sen. Joe Biden away from the Senate for seven months; a heart attack kept Sen. David Pryor, D-Ark., away from the Senate for five months.
And, even in poor health they can use their political will.
In the spring of 1964, Sen. Clair Engle, D-Calif., was partially paralyzed from surgery to remove a brain tumor but he refused to resign.
Dramatically, in June of that year -- one month before his death -- Engle was wheeled onto the floor of the Senate to break the filibuster of the Civil Rights Act. Unable to speak, he motioned towards his eye, signifying an "Aye" vote. It counted.
ABC News' George Stephanopoulos and Z. Byron Wolf contributed to this report