Mixed feelings on this. Not sure if it helps Trump or not.
I think it’s good to have just the two.
The math of whether a third party candidate would take more votes from Clinton or from Trump is far from certain, so I’m happy to put a damper on the whole third party effect.
Lots of undecideds are going to decide they’d rather have Trump if it is just Trump and Clinton on the stage.
For undecideds, I think having a third candidate on the stage is like staring at a menu with too many choices - they might remain undecided and cast their vote for the third party as a proxy for their ‘undecidedness’.
I’d rather force them to choose between the two.
Also, the optics of three on the stage would be unfavorable to Trump, as they would surely put Clinton the center.