The Trump campaign pays license fees to use these songs in public venues. The artists gets paid, and then wants the customer to not use the songs? I would call that fraud.
If the Prince Estate does not want the songs to be used that way, they should pony up the money and buy them back from whatever label that has authority to license them out.
Or they can shut up
Prince did legally acquire all of the publishing rights to the songs he recorded for Warner Brothers (1979-1996) in the Spring 2014. Since His death (April 2016), because he chose not leave a will or a trust, his ‘Estate’ had to be handled by the State of Minnesota, and the rights to his much of his catalog were recently acquired by Universal Music Group.