My guess is Bustos is holding out until 2020, if Durbin retires (as I think he will).
Speaking of Durbin, the Senate Dems really seem to be throwing him under the bus lately. What did he do to earn their ire?
If you're referring to Reid picking Schumer over Durbin, 538 said it was because Schumer has a closer voting record to Reid's, and also because Schumer is better at fundraising and has a bigger social media presence.
Not just that, but multiple people are encouraging Murray to challenge Durbin for the #2 spot, which seems odd considering he was a loyal soldier for not running against Schumer.
It seems to me that Durbin's milquetoast personality, better suited for an old Senate where Republicans had leaders like Howard Baker and Bob Dole, and his Old White Guy status have more to do with that than anything he did.