Sen. John McCain, who has been diagnosed with an aggressive brain tumor, told Sen. Lindsey Graham over the phone Wednesday that he’s “been through worse,” and then went on to discuss health care and other policy issues.

McCain, R-Ariz., talked about the long road ahead regarding treatments, but said that he has been through wars. Graham said McCain -- who is resting at his home in Arizona -- sounded resolved and determined.

“The disease has never had a more worthy opponent,” Graham said.

McCain was a prisoner of war in Vietnam for more than five years. Injuries from being tortured left the longtime Arizona senator unable to lift his arms above his head.

McCain, chairman of the Senate's Armed Services Committee, has glioblastoma, an aggressive cancer, according to doctors at the Mayo Clinic in Phoenix, where McCain had a blood clot removed from above his left eye last Friday.

It’s the same type of tumor that struck McCain’s close Democratic colleague in legislative battles, the late Sen. Ted Kennedy of Massachusetts.

The tumor digs tentacle-like roots into normal brain tissue. Patients fare best when surgeons can cut out all the visible tumor, which happened with McCain’s tumor, according to his office. That isn’t a cure; cancerous cells that aren’t visible still tend to lurk, the reason McCain’s doctors are considering further treatment, including chemotherapy and radiation.

In a statement on Twitter, the senator's daughter, Meghan McCain, spoke of the shock of the news and the anxiety over what happens next. “My love for my father is boundless and like any daughter I cannot and do not wish to be in a world without him. I have faith that those days remain far away,” she said.

News about the operation to remove a blood clot above his eye took many by surprise. Some theorized that McCain may have showed signs of a health issue during last month’s Senate questioning of former FBI Director James Comey. The senator appeared to struggle with his line of questioning. At one point, Comey said, “I’m a little confused, Senator.”

McCain blamed his vague questions on being tired from staying up late to watch an Arizona Diamondbacks game the night before.

A neurosurgeon downplayed the Senate hearing testimony as evidence of the condition, USA Today reported. Dr. Joseph Zabramski, a neurosurgeon, told the paper that McCain “was normal” after the hearing and does not see a connection.

As word spread of his diagnosis, presidents past and present along with McCain’s current and former Senate colleagues offered support in an outpouring rarely seen in Washington.

“Senator John McCain has always been a fighter. Melania and I send our thoughts and prayers to Senator McCain, Cindy, and their entire family. Get well soon,” President Trump said.

A group of senators prayed together Wednesday night after learning that McCain had been diagnosed with a brain tumor, according to one of the lawmakers.

Sen. John Hoeven, R-N.D., said he asked Sen. James Lankford, R-Okla., who has a master's degree in divinity, to lead the group in prayer.

"It was very emotional," Hoeven added. The group of senators was taking part in an evening meeting to discuss health care.

The Associated Press contributed to this report