WASHINGTON — Republican Sen. John McCain, who is battling brain cancer, is back home in Arizona after being treated for a viral infection and will miss the vote on the GOP tax bill.

The 81-year-old senator was admitted last week to Walter Reed Medical Center, where he was dealing with the side effects of his treatment for cancer. He returned to Arizona this past weekend where he will undergo physical therapy and rehabilitation at the Mayo Clinic.

His wife, Cindy, tweeted on Monday: "Nothing beats the feeling of being home in Arizona for the Holidays!" with a photo of a Christmas tree.

McCain's daughter, Meghan, tweeted on Sunday: "My father is doing well and we are all looking forward to spending Christmas together in Arizona."

In a brief statement on Sunday, McCain's office provided an assessment from Dr. Mark Gilbert, chief of neuro-oncology at the National Institutes of Health's National Cancer Institute.

"Senator McCain has responded well to treatment he received at Walter Reed Medical Center for a viral infection and continues to improve," Gilbert said. "An evaluation of his underlying cancer shows he is responding positively to ongoing treatment."

McCain expressed appreciation for his care and the outpouring of support and, according to his office, "looks forward to returning to Washington in January."

Now in his sixth Senate term, McCain underwent surgery in mid-July to remove a 2-inch (51-millimeter) blood clot in his brain and was diagnosed with glioblastoma.

President Donald Trump told reporters Sunday he had spoken to Cindy McCain.

"They've headed back, but I understand he'll come if we ever needed his vote, which hopefully we won't," Trump said after returning to the White House from Camp David. "But the word is that John will come back if we need his vote. And it's too bad. He's going through a very tough time, there's no question about it. But he will come back if we need his vote."

This week, the GOP will try to pass a sweeping $1.5 trillion tax package in the Senate with a razor-thin majority and all Democrats opposed to the legislation.

Republicans hold a slim 52-48 advantage in the Senate, and McCain and Sen. Thad Cochran, R-Miss., missed votes last week. The 80-year-old Cochran had a non-melanoma lesion removed from his nose earlier this week. He is expected to vote on the tax bill.

Republicans secured the support of Florida Sen. Marco Rubio and Tennessee Sen. Bob Corker last Friday for the tax measure, and they are poised to pass the bill by a narrow margin in the face of unified Democratic opposition. As a backstop, Vice President Mike Pence would be available to break a tie.

A vote is expected in the House on Tuesday and the Senate on Wednesday. If approved, the measure would head to Trump for his signature on what will be his first major legislative accomplishment since taking office 11 months ago.

After his summer surgery, McCain rebounded quickly, returning to Washington and entering the Senate on July 25 to a standing ovation from his colleagues.

In a dramatic turn, he cast a deciding vote against the Republican health care bill — a move that drew the wrath of Trump and conservatives. McCain's vote scuttled the seven-year effort by the GOP to dismantle much of President Barack Obama's health care law.

But McCain's condition has appeared to worsen in recent weeks. He suffered a minor tear in his right Achilles tendon, forcing him to wear a walking brace. McCain eventually began using a wheelchair, with members of his staff pushing him where he needed to go.

Associated Press writer Donna Cassata contributed to this report.