Trump is a recent enough phenomenon that there is no "established" way to refer to him as an adjective. I'm sure, right now, the legions of journalists are straining their brains to come up with the best witticism.
Be aware that these suffixes can imply different things. For example -ian means "One from, belonging to, relating to, or like." while -esque means "In the style or manner of" or "resembling".. A "Trumpesque" policy would be something like what Trump would do, but not an actual Trump policy.
As a side note, you might be interested to know that Trump supporters have been referred to as "trumpers", "trumpets", and (more pejoratively) "trumpsters", among others.
The clever part is to play off of another word, so that your resulting word has two (or more) meanings. "Trumpet" is a good one, because it's already the name of a loud, braying musical instrument. "Trumpster" plays off of the word "dumpster" (another word for "rubbish bin").
In the same way, if you want to come up with a clever word that means "of or like or relating to Trump" you need to consider words that sound similar or which have similar structure. TRomano suggests things like "trumpical" ("topical"? "tropical"?) or "trumptastic" ("fantastic"), so you can see how the process works.