As expected, Jon Kyl's placeholding days are at an end.
He agreed in September to serve in the late John McCain's seat, and as promised, will now resign as of December 31.
Arizona state law requires a vacant Senate seat to be filled by the party elected to hold it. It is likely that losing mid-term candidate Martha McSally will be asked to fill the seat.
It will be a permanent campaign mode seat, as whoever fills McCain's seat now must run in a special election in 2020 and then again in 2022 when McCain's actual term ends.