Despite an ongoing battle with brain cancer, Sen. Edward M. Kennedy vowed to continue his fight for national health care.
The Massachusetts Democrat has championed health care reform for decades and hopes to work with President Obama and Democrats who control Congress to forge a breakthrough in coming months.
"I'm looking forward to being a foot soldier in this undertaking and this time we will not fail," Kennedy said Thursday at a health care summit hosted by Obama.
Warm applause greeted Kennedy, back in Washington for the first time since casting a vote on the economic stimulus bill last month. Earlier this week it was announced that Kennedy is to be awarded an honorary knighthood by Britain.
"To Sir Edward Kennedy," Obama said amid laughter and applause from those gathered at the White House. "That's the kind of greeting a knight deserves."
Kennedy, who recently turned 77, is battling brain cancer and has been in Florida continuing his treatment and physical rehabilitation.
He chairs the Health, Education, Labor and Pensions Committee and was a strong Obama backer during the 2008 campaign.
Kennedy is to be feted Sunday at the Kennedy Center with a birthday concert salute.
The senator suffered a seizure at a legislative luncheon in the Capitol following Obama's inauguration in January, leaving many of his colleagues and friends shaken and worried. He returned to the Senate in February for a key vote on the economic stimulus package.
He plans to travel between Florida and Washington for Senate business until the weather gets warmer, aides have said.
Kennedy was diagnosed with a malignant brain tumor after he had a seizure in May while he was at his family's home in Hyannis Port, Mass. He underwent surgery in June.
Kennedy surprised his colleagues in July when he returned to Capitol Hill to vote on a Medicare bill. He also made an unscheduled appearance at the Democratic National Convention to rally Democrats for Obama. His speech drew a rousing response from delegates.
The Associated Press contributed to this report.