I wouldn't use the word isolationist. That would be inaccurate. Sending the U.S. Navy to trouble spots like the South China Sea is far from it.
The positioning of American armed forces is a much better indicator of a president's isolationism than are words coming out of pundits mouths, because the president is the commander-in-chief.
Isolationism is not about international trade policy, but isolating the country in other international relations, especially the political affairs of other countries. When Trump comments about Brexit or the Russian conflict with Ukraine, it is pretty clear he isn't an isolationist.
Trump's foreign trade policy hasn't really been isolationism, but an unwillingness to engage in certain relationships he feels are to the disadvantage of the country. Trade sanctions are distinct from isolationism.
If you look the word up in a dictionary, you will generally find it's properly used in the plural. Consider this typical definition (from Bing):
isolationists (plural noun)
a person favoring a policy of remaining apart from the affairs or interests of other groups, especially the political affairs of other countries.
Example (from the Oxford English Dictionary):
Those who would have us involved in a perpetual war of intervention invariably call those who are unenthusiastic "isolationists."
This above example show how labels like isolationist are typically misused in political context. Isolationism refers to a characteristic of polices, not people. A president can make some policy decisions which lean toward isolationism while simultaneously supporting other polices of interventionism.
To argue Trump is an isolationist is to invoke the informal fallacy of false dilemma. Such an argument has no place in reasoned thought.
George Washington, in his farewell address, famously advised against "foreign entanglements". While that aspect of Washington's address might be leaning toward isolationism, that doesn't necessarily make him a good example of being an isolationist, as he was also defending free trade and suggesting the federal government should be limited to defending the rights of American merchants.