(CBSNEWS) – Sen. John McCain is returning home to Arizona to begin radiation and chemotherapy treatment, following his decisive vote to block his party’s attempt to repeal parts of Obamacare.

The Arizona Republican will begin the treatment Monday at the Mayo Center in Phoenix, but keep his work schedule and plans to return after August recess, according to a Friday statement from his office. The 80-year-old senator was diagnosed with glioblastoma, an aggressive form of brain cancer, after doctors performed surgery on a blood clot above his left eye.

READ MORE: Texas Experiencing Another COVID-19 Surge

McCain’s vote was critical in Republican’s failure to pass a “skinny repeal” of Obamacare, as the bill failed by one vote in the 1 a.m. hour on Friday. McCain was one of only three GOP senators to vote against the measure — the others were Sen. Lisa Murkowski of Alaska and Sen. Susan Collins of Maine.

When reporters asked why he cast a “no” vote, McCain’s response was simple: “I thought it was the right thing to do.”

READ MORE: Administrative Court Judge Orders Mask-Wearing To Enter Dallas County Courthouses

A few hours after the middle-of-the-night vote, McCain was back to work in his office.

The prognosis for the type of cancer McCain has is grim, CBS News medical contributor Dr. David Angus told “CBS This Morning” last week.

“Glioblastoma is the most aggressive form of brain cancer,” Angus said. “Most people live about 14 and a half months.”

MORE NEWS: Summer Break Ends Early For Some Dallas ISD Schools