The top question surrounding Congress’ military policy decisions for 2018 is what role one of their most prominent defense voices will have in the months to come.

Sen. John McCain, R-Ariz., is chairman of the Senate Armed Services Committee and a key gatekeeper of military strategy and legislation on Capitol Hill. He is also an 81-year-old six-term senator battling brain cancer.

Shortly after his diagnosis in July, McCain said he planned to keep working through his chemotherapy, “giving many of you cause to regret all the nice things you said about me.”

And after extensive treatments during the summer recess, McCain returned to help shepherd the annual defense authorization bill through his chamber. He has sparred with Pentagon and White House officials in recent months over a lack of communication with Congress on military matters, vigorously reiterating lawmakers’ oversight responsibilities.

But he has also cut back on public appearances and been noticeably late to some committee hearings as his medical treatments continue. He missed the major tax reform vote at the end of the session to continue treatments back in Arizona, a sign for many around Congress that his health may be worsening.

Even a slightly less vocal McCain would present a major shift in defense policy discussions on Capitol Hill. The Navy veteran and former prisoner of war has been a frequent critic of President Donald Trump in the last year and often a quick counterpunch quote to the White House’s military announcements.

He has also been a driving force for Pentagon reforms for years, mandating a host of changes in procurement and management within the defense hierarchy. And as chairman of the armed services panel, he has set the pace for Trump’s defense nominees, sometimes slow-walking them in protest of other administration moves.

For now, McCain has given no indication he intends to change his legislative routine. Whether his age and illness will allow him to continue the demanding schedule he has maintained in recent years remains to be seen.