Announce the Human Mission to Mars, before the end of the Presidential term, use SpaceX obviously but also invite the adversaries Russia and China, and India, EU, others, to ALL PARTICIPATE.
This would quickly reduce all tensions, end all wars, give them significant roles to play as they wish in this international collaborative project. They can help to design and to build everything that’s inside the rocket, to sustain life in space, to have comfortable ride in space, rovers, more space suit designs, water recycling, space food, gamma ray protection systems, fuel generation systems on Mars and more. And the number of Astronauts going up would represented all the peoples of the world.
The Missions to the Moon and to elsewhere in the Solar System, would also all be collaborative.