Republican Sen. John McCain is returning to Arizona after spending several days in a Maryland hospital recovering from side effects from chemotherapy treatment for brain cancer, CBS News has learned.

McCain left Washington Sunday and is heading back to his home state to spend the holidays with his family. He will not be on hand for the final vote on the GOP tax passage expected for early this week. It is unclear when McCain might return to Washington.

Despite a razor-thin margin needed to pass the measure, McCain's presence will not likely be the determining factor in the vote. Two critical senators -- Bob Corker of Tennessee and Marco Rubio of Florida -- announced their support for the bill last week after initially saying they would oppose earlier versions.

GOP leaders aim to hold floor votes this week, with the House expected to take up the measure first on Tuesday.

President Trump returned to the White House on Sunday evening and told reporters that McCain is "going through a very tough time."

Mr. Trump also mentioned that "[McCain will] come back if we need his vote" and said that he spoke with Cindy McCain and wished her and John well.

McCain, 81, has been receiving treatment at Walter Reed National Military Medical Center in Bethesda, Maryland, since Wednesday. His son-in-law said on "Face the Nation" Sunday that McCain had been "in good spirits."

"I'm happy to say that he's doing well. The truth is that as anyone knows whose family has battled cancer or any significant disease that oftentimes there are side effects of treatment that you have. The senator has been through a round of chemo and he was hospitalized this week at Walter Reed," said Ben Domenech, a conservative writer and husband of Meghan McCain.

McCain's daughter later thanked supporters for their "kind words" in a Sunday afternoon tweet, echoing her husband's statement to CBS News that her father was "doing well" and was looking forward to "spending Christmas together in Arizona."