Sen. John McCain, R-Ariz., speaks after he received the Liberty Medal from the National Constitution Center in Philadelphia, Monday, Oct. 16, 2017. The honor is given annually to an individual who displays courage and conviction while striving to secure liberty for people worldwide. (AP Photo/Matt Rourke)
PHOTO: Matt Rourke/AP
Sen. John McCain, R-Ariz., speaks after he received the Liberty Medal from the National Constitution Center in Philadelphia, Monday, Oct. 16, 2017. The honor is given annually to an individual who displays courage and conviction while striving to secure liberty for people worldwide. (AP Photo/Matt Rourke)
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WASHINGTON, DC - SEPTEMBER 1: Cindy McCain looks on as a joint military service casket team carries the casket of the late Senator John McCain following his funeral service at the Washington National Cathedral, September 1, 2018 in Washington, DC. Former presidents Barack Obama and George W. Bush delivered eulogies for McCain in front of the 2,500 invited guests. McCain will be buried on Sunday at the U.S. Naval Academy Cemetery. (Photo by Drew Angerer/Getty Images)
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Secretary of Defense James N. Mattis and Chairman of the Joint Chiefs of Staff Marine Gen. Joseph F. Dunford Jr. will brief the media on Tuesday, Aug. 28, at 10 a.m. EDT, in the Pentagon Briefing Room (2E973).  DAILY SCHEDULE: Secretary of Defense James N. Mattis and Chairman of the Joint Chiefs of Staff Marine Gen. Joseph F. Dunford Jr. brief the media at 10 a.m. EDT in the Pentagon Briefing Room (2E973). Both U.S. and foreign journalists without a Pentagon building pass must be pre-registered in the new Pentagon Visitor Management System to attend this briefing; plan on being escorted from the River Entrance Pedestrian Bridge or the Pentagon Metro Entrance Facility only. Please arrive no later than 45 minutes before the briefing; have proof of affiliation and photo identification. Please call 703-697-5131 for any questions and escort into the building. The briefing will also be streamed live on www.defense.gov/live.  Secretary of Defense James N. Mattis hosts an enhanced honor cordon welcoming Minister of Defense Ryamizard Ryacudu of Indonesia, to the Pentagon at 2:30 p.m. EDT on the steps of the River Entrance. All journalists desiring to cover the cordon must obtain a wristband from security screening. Journalists without a Pentagon facility access card must go through security screening at the base of the River Entrance Pedestrian Bridge, and will be escorted to the cordon from there. Security screening will begin at approximately 1:45 p.m. EDT; have proof of affiliation and two forms of photo identification. Journalists with a Pentagon facility access card, and whom have entered the building prior to 1:30 p.m. EDT, may go through security screening at the River Entrance to obtain their wristband. All journalists wishing to cover the honor cordon, including those with a Pentagon facility access card, must be in place no later than 2:15 p.m. EDT. Once security screening has been initiated at the base of the bridge, all journalists entering the building via the bridge for any reason, including those with a Pen
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(CNN) —  

Sen. John McCain returned to Arizona Sunday to continue recovering from the side effects of chemotherapy for a brain tumor and will not be in Washington for the tax vote this week, two sources close to McCain confirmed to CNN.

McCain is unlikely to return to Washington this year, one of the sources said. But his ability to get on a plane to Arizona was a “good sign,” a source said.

McCain left Walter Reed Medical Center “exhausted, but ok,” a Republican close to him said.

McCain’s daughter, Meghan McCain, confirmed that the senator would be in Arizona for Christmas.

“Thank you to everyone for their kind words. My father is doing well and we are all looking forward to spending Christmas together in Arizona,” she tweeted Sunday afternoon.

Dr. Mark Gilbert, chief of neuro-oncology at the National Institutes of Health’s (NIH) National Cancer Institute, released a statement Sunday saying McCain “continues to improve” after being treated for a viral infection. He added the senator is also responding positively to his ongoing cancer treatment.

McCain’s office released a statement Sunday night: “Senator McCain has returned to Arizona and will undergo physical therapy and rehabilitation at Mayo Clinic. He is grateful for the excellent care he continues to receive, and appreciates the outpouring of support from people all over the country. He looks forward to returning to Washington in January.”

The Republican senator was admitted into the hospital on Wednesday after missing a third straight day of votes in the Senate. McCain suffers from a type of brain tumor called a glioblastoma. He was diagnosed with the tumor following surgery to remove a blood clot in July.

The final vote on the Republican tax bill is expected to take place early this week.

The passage of the tax bill, however, does not hinge on McCain’s support because the GOP has a 52-48 vote advantage in the Senate. Vice President Mike Pence can also cast a tie-breaking vote, should it come to that.

The White House and Senate Majority Leader Mitch McConnell’s office have been planning for McCain’s potential absence during the tax bill vote, making Tennessee Republican Sen. Bob Corker’s announcement Friday that he would support the plan critical. He did so as an insurance policy for McCain’s absence, two Republicans close to the matter said.

Last week, sources in the Senate told CNN they were worried about McCain recently, following a week when the Arizona Republican was kept from the Senate to address side effects from his brain cancer treatment.

The sources described McCain as looking increasingly frail and said he has not spoken up in recent GOP meetings the way he had before, in addition to his absence this week for treatment at Walter Reed Medical Center.

CNN’s Ashley Killough, Ted Barrett and Phil Mattingly contributed to this report.