The years 1999 to 2012 hardly constitute "most of his adult life", but your point is still somewhat valid -- he was a businessman, never a politician.
It's also worth remembering the Democrat party turned on Trump with a vengeance, once his Republican affiliations became well known in 2015.
I don't remember Republicans ever attacking him like that when Trump was a Democrat.
That would be his political life Bro, and the point is valid; the Republican Party then, and now, is a hollow structure, filled with men dressed in seersucker suits and tasseled shoes. Hardly Trump. Hardly the American middle.