It would do a lot to change the minds of many people if Trump were to demonstrate antigravity on live television and promise to start producing units.
Because I do think antigravity is already known to be possible. The EM Drive is public knowledge and has been proven to produce anomalous thrust by NASA. Black projects are certain to exist and could have existed for a long time already. There is every reason to think that the EM Drive is far from the peak potential that could be achieved by actually understanding the new physics involved and engineering accordingly rather than just resorting to trial and error. Flying cars could become possibly. Space travel would be greatly changed. Even a weak, basic EM Drive would shorten greatly the time required to reach Mars, and a more advanced antigravity engine could make interstellar travel practical.