But the parties differ from one another, and from Mr. Trump, in critical ways. Rhetorically, Mr. Trump falls at a far end of the spectrum of right-wing politicians and parties that have not been shy about using openly racist or incendiary language to disparage immigrants and political opponents.

In some cases, like his calls to deport millions of undocumented immigrants, Mr. Trump has promised changes that many of his most adoring fans in Europe have stopped well short of.

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