With U.S. Sen. John McCain's death Saturday from a malignant brain cancer, what happens to Arizona's seat in the U.S. Senate? With the primary filing deadline passed, Arizona law is a gray area for some. We'll clear things up:

While the U.S. Constitution mandates that vacancies in the House of Representatives be filled by elections, it leaves to each state how to fill empty seats in the Senate.

In Arizona, the governor appoints an interim senator in the case of a vacancy. That senator serves through the next scheduled statewide general election, with the winning candidate in that vote serving the remainder of the original term in office, unless the original term was set to expire at that election.

Related: John McCain, longtime Arizona senator, dead at 81

The interim appointee must be of the same party as the vacating senator.

In McCain's case, if he were to have left office before March 31, Gov. Doug Ducey would have appointed a Republican to take the seat through November. There would be an election held in November to determine who would hold the seat through the end of 2022, when the seat would return to its regular six-year cycle of terms.

Arizona election law has been murky to some when it comes to filling a Senate seat after the primary filing deadline in an election cycle has passed. But the date at which a vacancy-filling election in the current year is precluded actually falls well before that. Even the people in Arizona Secretary of State Michele Reagan's office have repeatedly provided incorrect information, leading to widespread reports that are imprecise. The Washington Post, Roll Call, CNN, Arizona Daily Star and many others have published stories pegging the election/no-election date to May 30.

Why the confusion? The last date to file as a candidate in the primary election was the end of May, and the law in general mandates that any vacancy be filled at the next general election.

Court cases have repeatedly held that, under Arizona law, the "election" is held on Election Day, and that the term does not necessarily encompass the preceding process. Some officials have pondered if a special election could be ordered even after the May date.

But, a clause in the law clearly sets the deadline well ahead of the primary filing date. ARS 16-222 lays out that if a Senate vacancy occurs less than 150 days before the primary, an appointment shall be made and the seat held through the second general election following.

As McCain held his seat past March 31, any appointee named after that would serve through 2020. An election would then be held to determine the senator for the remainder of the term, through 2022. Unlike some states, Arizona does not hold special elections outside the regular every-two-years cycle of federal elections to fill Senate vacancies.

Complicating the politics of the situation in Arizona is the other Senate seat. U.S. Sen. Jeff Flake's term ends this year, which raised prospect of there being two Senate elections taking place at the same time.

Senators serve six-year terms, which are staggered so that only one-third of the entire body is up for election at a time. House members, by contrast, serve two years, with the entire group up for election every cycle.

McCain was reelected to a sixth term in 2016, with his term running through 2022. Flake was elected in 2012, with his term up this year.

If McCain's seat had become vacant after the November election, the interim appointee would serve through 2020, or the end of the term, depending on the timing of the appointment.

- 30 -