The "dilemma" he's referring to is the notion that Democrats might be better off not running a candidate and supporting "Independent" Sinema as the best chance of holding onto the seat.
This makes sense if you live in Washington. If you populate the real world, Sinema has a 0% chance of reelection whether the Democrats run a candidate or not. She's so incredibly unpopular, she cannot win, even heads-up against whatever fucking lunatic the Arizona GOP selects.
The only real question is whether Sinema will run as an independent and spoil the election for the Dems.