Is there an established adjectival form of (Donald) Trump?

There is strong supporting evidence that shows Trumpian is used in conjunction with the policies, ideas, and doctrines of the current President of US, Donald J. Trump.

Back in March 2016, before the Presidential elections were held in November that same year, the Republican candidate, Mitt Romney, said of Donald Trump's agenda

"Today, there is a contest between Trumpism and Republicanism," Mr Romney said. "Through the calculated statements of its leader, Trumpism has become associated with racism, misogyny, bigotry, xenophobia, vulgarity and, most recently, threats and violence. I am repulsed by each and every one of these."

In the same month, someone successfully foretold the following scenario:

With the Senate on his side, however, he could appoint Trumpian judges and justices […] If he refuses to appoint moderates demanded by the Senate, his advisers may be able to persuade civil servants to implement Trumpian policies but maybe not. (March 03, 2016) Quartz

From the right-wing British newspaper, the Financial Times

In a ranking of global financial centres last month, published by Z/Yen, London topped the think-tank’s league, a whisker above New York.
Little surprise there: London has led several league tables in recent years. But when Z/Yen publishes its index in a couple of years’ time — in a Trumpian world — there is a good chance those rankings will have changed. (NOVEMBER 17, 2016)

The ominous “Trumpian nationalism” started to gain territory

Like them or not, Trumpian nationalism and its intellectual cousins in Europe offer a new way of thinking about politics and public policy, which resonates among some of the electorate. (3 April 2017) CapX

Nearly one year into his presidency, liberal writers were using the term Trumpian in a derogatory sense.

New York Times columnist Thomas Friedman has likened it to a new Trumpian doctrine, "Obama built it, I broke it, you fix it." (Oct 28, 2017) The Record

It's Even Worse Than You Think by David Cay Johnston. Published, New York, 2018

Baker [liberal economist and press critic] noted two of many ways that Trumpian policies could boost corporate profits and thus raise stock prices while damaging the overall economy.

Forbes, the renowned American business magazine, appears to predilect Trumpian, 96 results over the noun form Trumpism, 53 results. While Trumpist (an adjective and also a noun) and Trumpesque (adjective) yield a miserly 9 hits and 2 hits respectively.

Harvard’s Larry Summers, former chief economic adviser to President Barack Obama, has expressed serious concern over Trumpian economics, citing the recent rising U.S. dollar as a major concern.

Last but not least, the entry for Trumpian was created by Wiktionary on 28 May 2010. Below is how the term was originally defined

Adjective
Trumpian (comparative more Trumpian, superlative most Trumpian)

Of or pertaining to Donald Trump (born 1946), American business magnate, socialite, author and television personality.

Today, Wiktionary's entry for Trumpian includes the following synonyms: Trumpish, Trumpesque, Trumpean, Donald Trumpian, Trumplike, Trumpite.

Interestingly, the entries for Trumpish and Trumpesque were created on 15 January 2016 just ten months before Donald Trump was elected into office but, more significantly, nearly six years after the term Trumpian had already been coined.

The suffixes -ian/-an and -ist have somewhat different meanings.

-ian / -an can mean when something relates specifically to a person, but -ist is typically used when something relates to an ideology.

So if Trumpism becomes more popular as a term maybe Trumpist will win out.

But I'm betting on Trumpian.