Generally speaking, it is considered polite to at least wait until the new Congress begins before one starts to speculate on who will be leaving it soon. It should be extra-exciting this year because there’s at least two Republican Senators (Paul and Rubio) who are eyeing the brassiest of brass rings – the Presidency – and both of them are up for re-election next year. Heck, both of them are freshmen. Two Democratic Senators are also contemplating their Presidential chances, too – Warren and Sanders – but I don’t think that either of them will quit the Senate in order to run, which is frankly sensible of them.
Should be fun! No, really. I love retirements. It messes up everybody else’s careful calculations, at least briefly. I feel that this is generally a good thing for people; teaches them that the whole thing can’t be turned into a spreadsheet.