Washington (CNN) -- Colleagues of Sen. Robert Byrd of West Virginia mourned his death as family and friends planned his funeral.
Byrd, the longest-serving member of the U.S. Congress, died Monday at the age of 92.
Under West Virginia law, the state's popular two-term Democratic governor, Joe Manchin, has the power to appoint Byrd's successor. Manchin is expected to name a fellow member of his party to succeed Byrd, who was also a Democrat, thereby keeping a total of 59 Democrats in the Senate.
There are questions, however, regarding exactly how long Byrd's appointed successor can serve before another election is held.
West Virginia law says that if a Senate vacancy is created within two and a half years of the end of a term, the appointed successor will automatically serve out the remainder of the term. If not, a special election is required.
Byrd's current term is scheduled to end on January 3, 2013. The two and a half year mark will be reached on Saturday, July 3.
West Virginia law fails, however, to state exactly when a vacancy occurs. Whether the vacancy is considered to have been created at the moment of Byrd's death, or when the Senate informs state officials of the vacancy, or when Manchin declares the seat vacant will be crucial. West Virginia -- a traditional Democratic stronghold -- has been increasingly competitive for the Republicans. John McCain easily defeated Barack Obama in West Virginia in the 2008 presidential election.
Neither Manchin nor the Democratic-led Senate have made any official declarations yet.
As question swirl around the timing of the next election for Byrd's seat, numerous political leaders have been issuing statements in remembrance of the nine-term senator:
-- President Barack Obama
"The people of West Virginia have lost a true champion, the United States Senate has lost a venerable institution, and America has lost a voice of principle and reason with the passing of Robert C. Byrd. Senator Byrd's story was uniquely American. He was born into wrenching poverty, but educated himself to become an authoritative scholar, respected leader, and unparalleled champion of our Constitution. He scaled the summit of power, but his mind never strayed from the people of his beloved West Virginia. He had the courage to stand firm in his principles, but also the courage to change over time."
-- Gov. Joe Manchin, D-West Virginia
"Sen. Byrd was a fearless fighter for the constitution, his beloved state and its great people. He made a significant mark as a member of Congress in both our state's and nation's history. His accomplishments and contributions will define history for eternity."
-- Sen. Jay Rockefeller, D-West Virginia
"It has been my greatest privilege to serve with Robert C. Byrd in the United States Senate. I looked up to him, I fought next to him, and I am deeply saddened that he is gone. He leaves a void that simply can never be filled. But I am lifted by the knowledge of his deep and abiding faith in God, I have joy in the thought of him reunited with his dear (late wife) Erma, and I am proud knowing that his moving life story and legacy of service and love for West Virginia will live on.
Senator Byrd came from humble beginnings in the southern coalfields, was raised by hard-working West Virginians, and triumphantly rose to the heights of power in America. But he never forgot where he came from nor who he represented, and he never abused that power for his own gain."
-- Senate Majority Leader Harry Reid, D-Nevada
"By virtue of his endurance, Robert Byrd knew and worked with many of the greats of the United States Senate. Because of his enduring virtue, he will be remembered as one of them. Senator Byrd dedicated every single day of his Senate service to strengthening the institution, state and republic that he loved so dearly. There will never be another like him."
--Senate Minority Leader Mitch McConnell, R-Kentucky
"Sen. Byrd combined a devotion to the U.S. Constitution with a deep learning of history to defend the interests of his state and the traditions of the Senate. We will remember him for his fighter's spirit, his abiding faith, and for the many times he recalled the Senate to its purposes. ... We are glad to know that Senator Byrd and his beloved Erma are reunited. We extend our deepest sympathies to the entire Byrd family."
--Sen. Patrick Leahy, D-Vermont
"No senator came to care more about the Constitution or to be a more effective defender of our constitutional government than the senior senator from West Virginia. He was a senator's senator. ... I know him as a mentor and a friend. I was honored to stand with him and fight against assaults on the Constitution and against an unnecessary and costly war in Iraq.
He was a self-educated man who learned much throughout his life and had much to teach us all. He was a symbol of West Virginia, he was an outstanding senator, and he was extraordinary American."
--Sen. Jeff Sessions, R-Alabama
"It is a sad day for all of us. There was no one who loved the institution of the Senate more, and no one who was a better student of it."
CNN's Ted Barrett, Alan Silverleib, and Paul Steinhauser contributed to this report.