WASHINGTON (AP) - Democratic Sen. Tim Johnson of South Dakota was in critical but stable condition Thursday after late-night emergency brain surgery, creating political drama about which party will control the Senate next month if he is unable to continue in office. Johnson suffered from bleeding in the brain caused by a congenital malformation, the U.S. Capitol physician said, describing the surgery as successful. The condition, present at birth, causes tangled blood vessels.
"The senator is recovering without complication," the physician, Adm. John Eisold, said. "It is premature to determine whether further surgery will be required or to assess any long-term prognosis."
Eisold said doctors had to drain the blood that had accumulated in Johnson's brain and stop continued bleeding.
Democrats hold a fragile 51-49 margin in the new Senate that convenes Jan. 4. If Johnson leaves the Senate, the Republican governor of South Dakota could appoint a Republican—keeping the Senate in GOP hands with Vice President Dick Cheney's tie-breaking power.
Johnson's condition, also known as AVM, or arteriovenous malformation, causes arteries and veins to grow abnormally large and become tangled.
The senator's wife, Barbara Johnson, said the family "is encouraged and optimistic."
In a statement from Johnson's office Thursday, she said her family was "grateful for the prayers and good wishes of friends, supporters and South Dakotans."
A person familiar with Johnson's condition said the 59-year-old senator's underlying condition caused the stroke-like symptoms and doctors will be watching him closely for the next 24 to 48 hours. The person spoke on condition of anonymity out of respect for the senator's family.
Senate Democratic leader Harry Reid of Nevada visited Thursday morning. He had visited the night before as well.
The emergency surgery lasted past midnight Wednesday
Apart from the risk to his health, Johnson's illness carried political ramifications, coming so soon after the Democrats won control of the Senate. If he were forced to relinquish his seat, a replacement would be named by South Dakota's GOP Gov. Mike Rounds.
A Republican appointee would create a 50-50 tie, and allow the GOP to retain Senate control.
Rounds' press secretary, Mark Johnston, said Thursday the governor was watching events and had nothing new to say.
"We're watching as much as everyone else," he said. "The most important thing is making sure Sen. Johnson is OK."
President Bush awoke Thursday to news of Johnson's condition, said first lady Laura Bush. "We're praying like I know all the people of South Dakota are for his very, very speedy recovery," Mrs. Bush told CBS's "Early Show."
Johnson, who turns 60 later this month, was admitted to George Washington University hospital at midday after experiencing what his office initially said was a possible stroke.
His spokeswoman, Julianne Fisher, later told reporters that it had been determined that the senator had suffered neither a stroke nor a heart attack.
Johnson became disoriented during a conference call with reporters, stuttering in response to a question.
Before he ended the call, Johnson appeared to recover and asked whether there were any additional questions.
Fisher said he then walked back to his Capitol office but appeared to not be feeling well. The Capitol physician came to his office and examined him, and it was decided he should go to the hospital.
He was taken to the hospital by ambulance around noon, Fisher said.
"It was caught very early," she said.
In its earlier statement, Johnson's office had said he had suffered a possible stroke and was "undergoing a comprehensive evaluation by the stroke team."
Johnson is up for re-election in 2008.
In 1969, another South Dakota senator, Karl Mundt, a Republican, suffered a stroke while in office. Mundt continued to serve until the end of his term in January 1973, although he was unable to attend Senate sessions and was stripped of his committee assignments by the Senate Republican Conference in 1972.
Johnson, who was elected in 1996, holds the same seat previously held by Mundt.
South Dakota Secretary of State Chris Nelson said there were no special restrictions on an appointment by the governor and a replacement would not have to be from the same political party.
Johnson, a centrist Democrat, was first elected to the Senate in 1996 after serving 10 years in the House. He narrowly defeated Republican John Thune in his 2002 re-election bid. Thune defeated Sen. Tom Daschle, the former Senate Democratic leader, two years later.
Johnson underwent prostate cancer treatment in 2004, and subsequent tests have shown him to be clear of the disease.
Johnson is the second senator to become ill after the Nov. 7 election. Wyoming Sen. Craig Thomas, a Republican, was diagnosed with leukemia on Election Day. He is back at work.
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Associated Press writers Laurie Kellman and Natasha Metzler in Washington and Dirk Lammers in Sioux Falls contributed to this report.
