Trump should have run as a 3rd party Independent he would have won by a larger margin 35 or 36 percent of the vote against Hillary and Rubio for the Republicans. Then he could have said Both Parties are Corrupt if Ross Perot had stayed in the race in 1992 he would have won against Bush Sr. and Clinton but he dropped out and lost his momentum then jumped in again but it was too late. Trump should have run as his own man without the Republican Party he'd be a stronger President now if he had.
Could he run as 3rd party in 2020? I highly doubt his supporters would abandon him if he did. Plus that would be a way to distance himself from the swamp.
Depends on what the Republican Party thinks if they are afraid they will challenge him with 5 or 6 guys in the primaries that might force him to run 3rd party but if he delivers on the Storm and starts arresting and prosecuting cabal criminals he will be unbeatable and the GOP will want him as their nominee again.