The priest may be concerned about appearing to be too political if he has to get up there and announce the Mass is being said for Donald Trump, or place such a request in the parish bulletin. He may also feel the Mass request was politically motivated in order to get the name of Donald Trump out in public associated with his parish.
If you genuinely want to have a Mass said for Donald Trump, do the prudent thing and send the request to the missions. I am sure a priest in a poor part of Asia somewhere will happily say Mass for Donald Trump and will be grateful for your stipend.
I agree Trump needs Masses said for him. I will request a couple this weekend. Thanks for the idea.
Edited to add, I wouldn’t be surprised if certain parishes have a policy of turning down all Masses requested for politicians or political people, unless of course said people are parishioners.