Complex sentence: Donald Trump's presidential candidacy has been extremely popular amongst groups which classify themselves as White Nationalists, White Supremacists, Neo-Fascists, or Neo-Nazis many of whom have claimed that Trump's candidacy has greatly boosted their popularity and aided their recruitment.
Split into simpler sentences: Donald Trump's presidential candidacy has been extremely popular amongst groups which classify themselves as White Nationalists, White Supremacists, Neo-Fascists, or Neo-Nazis. Many of these groups have claimed that Trump's candidacy has greatly boosted their popularity and aided their recruitment.