CHICAGO (AP) -- Whether Sen. Mark Kirk's recovery from a stroke takes weeks or months, the routine work of his office should continue with little interruption. It's a different story for some high-profile duties, however.
The first-term Republican's staff can respond to constituent problems and monitor issues. His Senate colleagues are likely to lend a hand, as they have for others who were absent for long periods. And with one Illinoisan in the White House and another in a top leadership position in the Senate, the state's interests aren't in danger of being overlooked.
"I wouldn't say a place can run fine without the boss, but there are some things you can do," said Mark Kimble, spokesman for Arizona Rep. Gabrielle Giffords, who was nearly killed in a shooting last year and announced her resignation over the weekend.
Kirk's absence undoubtedly will create a hole. His staff can't vote for him, after all, and they can't speak out like he did on some key issues, such as Kirk's calls for strong Iran sanctions.
Kirk, 52, suffered a stroke over the weekend. He underwent surgery Sunday night that included removing a portion of his skull to relieve pressure from swelling. Doctors hope the swelling subsides in the coming days, giving them a better idea of the damage done by the stroke.
Dr. Richard Fessler at Northwestern Memorial Hospital, who performed Kirk's surgery, said the odds of a full mental recovery are good. Kirk appeared to recognize those around him and is responding to commands, Fessler said Monday. But the surgeon warned it will be "very difficult" for Kirk to regain movement in his left arm and that his left leg and face also might be affected.
"The prospects for his full physical recovery, particularly on the left side of his body, are not great," Fessler added.
It's not unusual for ailing senators to be absent from the Capitol for long periods.
Sen. Tim Johnson, D-S.D., suffered a brain hemorrhage in December 2006, spent several weeks in a coma and did not return to Washington until the following fall. His speech was a bit slurred and he sometimes he used a scooter to get around, but Johnson won re-election and now chairs the Banking Committee.
Drey Samuelson, his longtime chief of staff, said the office ran smoothly for the most part during Johnson's absence. Aides helped constituents with issues like Social Security problems and answered letters. To a degree, they could also work with other senators on legislation.
But without Johnson at the helm, there were limitations on what his aides could accomplish.
"There's a vacuum when the guy that's the center of the office isn't there, and isn't there for nine months," Samuelson said. "I had a pretty good idea, but I'm not the senator and I wanted to be sure that I knew what he wanted to do."
A statement from Kirk's office Monday evening said: "As Senator Kirk begins his recovery, his office will remain open to constituents. The staff will continue to provide the same level of service and dedication to the residents of Illinois as they have for the last year."
In Washington, Kirk's absence would mean one less Republican vote in a Senate with a 51-47 advantage for Democrats. And it could be felt in the effort to impose sanctions on Iran, an issue on which he has been very vocal.
Late last year, Kirk, a member of the powerful Appropriations Committee, joined forces with Democratic Sen. Bob Menendez of New Jersey in imposing crippling sanctions on Iran. The two senators sponsored an amendment to the annual defense bill that targets foreign financial institutions that do business with the Central Bank in Tehran. In a rare unanimous vote, the Senate backed the measure 100-0.
President Barack Obama signed the wide-ranging defense bill with the sanctions on New Year's Eve. The administration is scheduled to release proposed rules on those sanctions in the coming weeks.
Over the weekend, Kirk had reported feeling dizzy and checked himself into Lake Forest Hospital before being transferred to Northwestern. Tests showed he had a tear in the carotid artery on the right side of his neck. Carotid arteries carry blood to the brain, and carotid tears are a common cause of strokes in people in their 50s or younger.
Fessler, Kirk's surgeon, described the senator as "young, very healthy and in good shape."
"Sen. Kirk's job is cerebral, and I believe the functions required to do his job are going to be fine," said Fessler, a neurosurgeon who removed a 4-by-8-inch piece of Kirk's skull Sunday night.
Dr. Joseph Broderick, a University of Cincinnati stroke expert, said that when removing part of the skull is required, "that is a pretty significant stroke" that likely has caused substantial damage.
"Those people almost always will have some type of deficit long-term. Some may get back to being functional, but some are left with very severe deficits," said Broderick, a fellow of the American Academy of Neurology.
Kirk's family said in a statement that he had "always shown great courage and resilience and we are confident that the fighter in him will prevail."
Associated Press writers Lindsey Tanner in Chicago, Christopher Wills in Springfield, Chet Brokaw in Pierre, S.D., and Andrew Taylor and Donna Cassata in Washington contributed to this report.