Pacquiao had been offered an April 22 clash by promoter Bob Arum and seemed to be on the verge of accepting until interest came from the Middle East for a deal worth a reported $38 million.
With the United Arab Emirates firmly in the driving seat, Horn was pushed out in favor of Pakistani-Brit Amir Khan, although Arum has reservations about whether the money will actually be forthcoming.
Horn, with the help of the Australian government, has a guarantee in place, and with Trump backing his efforts, the 29 year-old is hopeful the fight can still go ahead in the spring.
Watch the video provided by Duco Events, which includes a social media post by the President himself.