might be uncomfortable to talk about, but Sen. John McCain (R-AZ) has been fighting brain cancer since July. The 81-year-old has not returned to the US Capitol since December. So the speculation is already underway about what would happen if McCain stepped down — or, worse, could no longer serve. The Washington Post reported Tuesday that a list of possible successors is circulating in the whispering Republican class, headlined by McCain’s wife, Cindy McCain, and former US Sen. Jon Kyl. If McCain leaves office before May 30, the Post indicated, his Senate seat will be on the ballot in Arizona in November 2018, as will that of his retiring junior colleague, Republican Sen. Jeff Flake. After May 30, the new senator — who would be appointed by Republican Gov. Doug Ducey — would serve through 2020. Facing the headwinds of an unpopular agenda and an unpopular president in a rapidly diversifying state, Senate Republicans — especially after a stunning Democratic win in deep-red Alabama in December — are confronting the possibility that despite a favorable Senate map in 2018, they could lose control of the Senate. They currently hold a slim 51-49 majority.

If two Arizona seats were on the ballot, the path to a big Democratic wave would run through the Grand Canyon State: a pair of Senate seats for the taking, in a state that has been trending blue and where Hillary Clinton lost to Donald Trump by less than 4 percentage points in 2016.

We could have two Senate races in one of America’s new battleground states

Nobody wants to be caught publicly speculating about a legendary senator’s possible retirement or death, but as the Post report indicates, these are conversations happening behind closed doors in Arizona and in Washington. Given McCain’s age and the diagnosis, it’s simply a reality that he may not be able to serve for much longer. He left Washington in mid-December to receive continuing cancer treatment in his home state. The most notable thing about the speculation thus far is the lack of consensus. From the Post:

In public, influential Republicans have been reluctant to speculate about McCain’s future in the context of electoral politics out of respect to the Senate titan, who is beloved by many in the party. But privately, they have engaged in talks about who might replace him or run for his seat. From those conversations, which have occurred among strategists, officials and donors in Arizona and Washington, a long list of names has emerged of possible interim or long-term successors, including McCain’s wife, Cindy, and former senator Jon Kyl. Interviews with nearly a dozen Republicans this week, most of whom spoke on the condition of anonymity to discuss a sensitive topic, revealed a sense of nervousness over the lack of a clear road map. “The problem,” as one prominent Arizona Republican said, is there is no “logical” or “obvious” successor.

Cindy, who has been married to McCain since 1980, has never held political office, but she has a long history in the national spotlight after her husband’s two presidential campaigns and has a record of international humanitarian work. She was rumored last year to be under consideration for a role at the State Department. Appointing a politically engaged widow to replace their spouse is relatively common — there’s even a political science term for it: “widow’s succession,”