Former U.S. President George H.W. Bush has been moved to an intensive care unit at a hospital in Houston, Texas.
The former president, 88, was admitted to the hospital last month suffering from bronchitis. His spokesman says Bush was moved to the intensive care unit Sunday after a "series of setbacks," including a persistent fever. The spokesman says Bush continues to be alert and that doctors are "cautiously optimistic" about his treatment.
The former president's wife, Barbara, and a son and grandson spent Christmas Day with Bush.
Bush served as the 41st U.S. president from 1989 to 1993. The highlight of his presidency was the international coalition he assembled that drove Iraqi forces out of Kuwait in 1991.
Bush also served as a congressman, ambassador to the United Nations, ambassador to China and director of the CIA. He was vice president from 1981 to 1989 under the late President Ronald Reagan.
His sons include the 43rd president, George W. Bush, and former Florida Governor Jeb Bush.
George W. Bush, left, is shown with his father, George H.W. Bush in this photo from 1968.
George H. W. Bush raises his right hand as he is sworn into office as the 41st president of the United States by Chief Justice William Rehnquist outside the west front of the Capitol on January 20, 1989.
This June 25, 1990 photo shows then President George H. W. Bush greeting then African National Congress Deputy President Nelson Mandela at the White House.
This October 15, 1992 photo shows then President George H. W. Bush, talking with independent candidate Ross Perot as Democratic candidate Bill Clinton stands aside at the end of their second presidential debate in Richmond, Virginia.
This January 3, 1993 photo shows then Russian President Boris Yeltsin toasting with then U. S. President George H. W. Bush after they signed the START II treaty in Moscow.
This November 9, 1988, photo shows President-elect George H. W. Bush holding his hands up to acknowledge the crowds applause, and ask them to allow him to continue his speech during his victory rally with grandson, George P. Bush, right, and son, George W. Bush.
Then President George W. Bush and Laura Bush leave Saint John's Church with former President George H. W. Bush and Barbara Bush after attending Sunday service,Washington, January 27, 2002.
Former President George W. Bush sits with former presidents and their wives during funeral services at the National Cathedral in Washington on June 10, 2004 for former President Ronald Reagan.
Former President George H. W. Bush looks up with his wife, Barbara and granddaughters Barbara, left, and Jenna as they walk through the Capitol Rotunda for George W. Bush's innauguration ceremony, January 20, 2005.
Former Presidents Bill Clinton, left, and George H. W. Bush smile at each other on the podium at the Tulane University Commencement in New Orleans, Louisiana, May 13, 2006.
Then President George W. Bush casts over his father, former President George H. Bush, left, while fishing near Kennebunk, Maine, June 29, 2007.
Then-President George W. Bush poses with President-elect Barack Obama, and former presidents George H.W. Bush, Bill Clinton and Jimmy Carter, January 7, 2009, in the Oval Office of the White House.
Former President George H. W. Bush rides tandem with Sgt. Michael Elliott of the Army Golden Knights parachute team as he celebrates his 85th birthday with a parachute jump, June 12, 2009, in Kennebunkport, Maine. (Army Golden Knights)
Former President George H. W. Bush, right, former Secretary of State James Baker, left, and Houston Texans owner Bob McNair pose together before an NFL football game against the Buffalo Bills in Houston, November 4, 2012.