"It is not conscionable to tell young people who came here as children that they have to go back to a country that they don't know," McCain said on CNN's "State of the Union."
McCain, the chairman of the Senate Armed Services Committee, pointed out that nearly 900 of these so-called "Dreamers" serve in the military.
"Now, are we going to go to a young man or woman serving in Afghanistan or Iraq today and say, 'Hey by the way, you're a Dreamer, get back to (your birthplace)?" McCain asked.
DACA, which was created by executive order, needed to be guaranteed through legislation and should include a path to citizenship, but those measures should be passed as part of a broad, comprehensive immigration reform bill, McCain said. The Arizona Republican pointed to a comprehensive immigration overhaul previously passed by the Senate, but not the House, as evidence the parties can get together on the issue.
"We did it once in the Senate," McCain said. "We can do it again in a bipartisan fashion."
Republicans not doing enough
In his appearance Sunday, McCain expounded on a message he has delivered loudly since his diagnosis: that the Senate should produce legislation through open, bipartisan debate and that Republicans have not used the massive power granted to them by the people effectively enough.
As things stand, Republicans have not been able to translate control of both chambers of Congress and the White House into substantial changes for the country, he said, summarizing their accomplishments as the confirmation of Supreme Court Justice Neil Gorsuch and the undoing some Obama-era regulations.
"That's what they see with nine months of undivided Republican majorities," McCain said. "That's not good."
He blasted the process Republicans used, unsuccessfully so far, to try to repeal and replace much of Obamacare.
"Why didn't we have hearings, have amendments, have debate, bring a bill to the floor?" McCain asked.
He called for an open debate on health care and other major issues facing the country, like immigration and government appropriations.
Shortly after his diagnosis, McCain returned to the Senate as the chamber debated health care. Although he voted to start debate on a so-called "skinny" repeal of Obamacare, McCain was one of three
Republicans to join Democrats in opposing the measure, a near-miss that effectively ended the Senate Republicans' health care push.
Before the Senate came back into session this month, McCain penned an op-ed
calling on Congress to serve as a check on President Donald Trump, who McCain said is "often poorly informed" and "can be impulsive."
In Sunday's interview, McCain also lightly parted ways with much of his party on climate change, acknowledging the threat it poses just as Hurricane Irma began to hit the state of Florida.
Asked why a wide swath of his party denied the scientific community's conclusions about climate change, McCain answered, "I don't know."
He added that he believed nuclear power would be one element of an effective strategy on climate change and mentioned the economic benefits of new energy technologies, like solar energy, in his home state of Arizona.
"We have to understand that the climate may be changing," McCain said. "We can take common-sense measures."
Calls for increased defense spending
McCain criticized Trump's recent deal with Democratic leaders to tie funding for hurricane relief to three-month extensions of spending and the debt ceiling, saying it didn't reflect the bipartisan approach he had in mind.
"This was not an exercise in bipartisanship," McCain said. "The Republican leaders, (House Speaker Paul) Ryan and (Senate Majority Leader Mitch) McConnell, were surprised to hear that he had cut this deal with Chuck and Nancy."
McCain, who voted against the agreement, said it was wrong to tie the hurricane money to a resolution to continue current federal spending levels. A spending deal should have been negotiated and should have included billions more for the military, he said.
"I believe my first obligation as chairman of the Armed Services Committee is to make sure the men and women who are serving in our military have everything they need," McCain said. "Under this agreement, they not only don't have everything they need, their lives are in greater danger."
Pointing to foreign threats, McCain called for a robust and aggressive posture against North Korea. He argued for more pressure on China, improving relations with Japan and South Korea and increasing missile defense. The Republican hawk also said it was worth considering deploying nuclear weapons to the Korean Peninsula.
'I'm facing a challenge'
McCain sought to present his brain cancer diagnosis in a positive light, calling it the latest in a lifetime of tough fights and one he believed he could win.
"I'm facing a challenge, but I've faced other challenges," McCain said. "And I'm very confident about getting through this one as well."
McCain said he felt fine, even energetic, after his treatment and would be receiving a magnetic resonance imaging test on Monday.
But while he said he was receiving first-class medical treatment, he emphasized that he did not want to paint a "rosy picture" for what he said is a tough form of cancer.
The former presidential candidate and storied prisoner of war was reflective when asked about his condition, looking back on his life as one worth celebrating and calling his underdog bid for the Republican nomination in 2000 one of his many joyous memories.
Asked how he wanted to be remembered, McCain said of himself: "He served his country, and not always right -- made a lot of mistakes, made a lot of errors -- but served his country, and I hope we could add, honorably."