Sen. John McCain (R-Ariz.) speaks with reporters outside of his office in the Russell Senate Office Building on Sept. 5 in Washington. (Oliver Contreras/For The Washington Post)

John McCain is not your typical brain cancer patient.

It has been 48 days since the Republican senator from Arizona announced his diagnosis and 18 days since he completed his first round of chemotherapy and radiation treatments.

Now, far from shrinking from public life, McCain is back on Capitol Hill with the rest of the Senate, ready to manage the floor debate over a defense authorization bill and begin the work of an extraordinarily busy and consequential month in Washington.

McCain, 81, was spotted in the halls of Congress ahead of the Senate’s first votes since members departed for their home states on Aug. 3. His last memorable act before the break was to cast the decisive “no” vote against the Republican health-care bill, delivering a dramatic thumbs-down on the Senate floor as GOP leaders watched, aghast.

Those leaders might not have been pleased with his health-care vote, but they publicly welcomed McCain’s return this month, given the ongoing work on the National Defense Authorization Act, which McCain oversees as head of the Armed Services Committee.

Senate Majority Leader Mitch McConnell (R-Ky.) tacitly acknowledged McCain’s illness Tuesday and predicted that he would manage the defense measure with “skill and dedication.”

Votes on the bill have not yet been scheduled.

“We’ve kept Senator McCain and his family in our thoughts over the state work period,” McConnell said on the Senate floor. “We’re glad to have him back with us.”

The Arizona Republican learned he had cancer in July after undergoing surgery to remove a blood clot above his left eye. Lab tests after the procedure revealed the existence of a glioblastoma, an aggressive form of brain cancer.

Since announcing his diagnosis on July 19, McCain has worked to maintain a steady public schedule, holding regular meetings with Arizona leaders and giving interviews to local media outlets, according to his social media accounts.

McCain attended policy events in Arizona and abroad over the recess, traveling to Cernobbio, Italy, for an international economic forum last week and speaking at an Arizona State University cybersecurity conference the week before. And he kept up a stream of commentary on such events as the violence in Charlottesville and President Trump’s pardon of former sheriff Joe Arpaio, which he said “undermines his claim for the respect of the rule of law.”

The NDAA will be McCain’s primary legislative focus this month. But his presence will also be helpful as Republican leaders gather support for crucial votes, such as raising the debt ceiling, funding the government and perhaps responding to Trump’s suspension of protections for undocumented immigrants brought to the United States as children, which McCain called “unacceptable” on Tuesday.

McCain has said repeatedly that he doesn’t plan to miss major business in the Senate.

“This is a very malicious disease. But I’ve had other challenges in my time, as well,” McCain told constituents during a Facebook Live event last month.

“I don’t mean to be repetitious, but to my Democrat friends and some of my Republican friends: I’m coming back,” he said.