Actually, Trump isn't like those who supported the war in Vietnam.  Those who supported the war were not isolationists.  On the contrary, they were hardline Cold-Warriors, determined to do battle with the Russians everywhere - even in outer space.
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Trump is much more like the isolationist and nationalist "America Firsters" from 1940, or one of the "Know-Nothings" or "Coppeheads" of the US Civil war.
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Those streaks in American culture, and the streak of virulent racism in white protestants, both have long histories pre-dating Vietnam.
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Keep in mind that to keep his broad coalition together, FDR at the height of his power was nonetheless unable to pass an anti-lynching law.
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Long before Vietnam.