The purpose of that pledge is a psych op to make the preposterous sound less preposterous.
I like the way Trump answers - yes, I’ll support the winner because it will be me.
Then, when they follow up and say - but what if it’s not you - will you support them?
His answer is - but that won’t happen because it will be me.
Then Bret Bair or whoever will say - so that’s a “no”? You won’t support the winner of its not you?
Then he doubles down and says - No, it’s a “Yes” I will support the winner which will be me.
The way Trump supporters have to twist themselves into illogical knots just so they don’t have to actually answer a question constantly amazes me.