[Cletus.D.Yokel]

GITMO...keep it open and use it for her.

Or, use it further?

I hear for her.

Normal pronunciation for “further” has emphasis on the first syllable; /FUR/ther.
Trump’s emphasis was on the second vocabule; for /HER/.

[HoneysuckleTN]

GITMO...keep it open and use it for her. etc.

I think it's "for her", too. I haven't listened to the whole speech yet, but I have listened to that bit a few times. The rest of what he says around that is loud, distinct, and clearly spoken, before and after. As he goes into "keep it open..." his voice gets lower and lower, as if he's adding "and use it for her" under his breath. IMO, no reason for him to add it under his breath if it's "further".