Senator John McCain is returning to Arizona Sunday after spending time at a Maryland medical facility earlier this week as he battles cancer treatment side effects.

Sen. McCain is not expected to be in Washington for the tax vote, CNN confirmed. The final vote on the Republican tax bill is slated for sometime this week.

Republicans secured the support of Sens. Marco Rubio of Florida and Bob Corker of Tennessee last week and should have enough votes for the GOP measure.

His daughter, Meghan McCain, took to Twitter on Sunday saying that she is excited to spend Christmas with her dad in Arizona.

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. If you’re feeling charitable this Christmas @HeadfortheCure or @NBTStweets to help find a cure for brain cancer is what I recommend. ❤️ — Meghan McCain (@MeghanMcCain) December 17, 2017

On Wednesday his office released a statement saying he is receiving treatment at Walter Reed Medical Center for “normal side effects” of his ongoing cancer treatment.

"Senator McCain is currently receiving treatment at Walter Reed Medical Center for normal side effects of his ongoing cancer therapy. As ever, he remains grateful to his physicians for their excellent care, and his friends and supporters for their encouragement and good wishes. Senator McCain looks forward to returning to work as soon as possible."

Sources tell news outlets that Sen. McCain has been looking increasingly frail and has not spoken up during recent GOP meetings.

President Trump told reporter's on Sunday that he spoke to McCain's wife, Cindy, and wished the couple well.

"They've headed back, but I understand he'll come if we ever needed his help, which hopefully we won't," Trump said.

He was first diagnosed with brain cancer this summer.

"He's going through a very tough time, there's no question about that," Trump said.

Dr. Mark Gilbert, Chief of Neuro-Oncology at the national Institute of Health's National Cancer Institute, released the following statement regarding Senator McCain's condition:

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

The office of Senator McCain also released the following statement Sunday afternoon:

“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.”