"If Obama had been a leftist, the GOP's policy of negating him on every issue might have positioned Republicans in the mainstream. Instead, because Obama was a moderate, the GOP's negation strategy pushed it toward the fringe. Obama was for fiscal responsibility and compromise, so Republicans were for absolutism and drama, risking a federal shutdown and a credit default. Obama was for respecting the Supreme Court, so the GOP was for defying judicial orders. Obama was for using sanctions to pressure Iran into a nuclear deal, so Republicans were for scrapping the deal and daring Iran to provoke a war. Obama, like Bush, was for drawing a clear distinction between terrorists and Muslims. So Republicans were for blurring that distinction.
"In Trump, Republican voters have found their anti-Obama."
William Saletan in Slate explains the rise of Donald Trump.
And Jamelle Bouie defines "Trumpism" as "a familiar movement in American life."