Shane Claiborne was referring to the support of former Grand Wizard David Duke, which he gave during his own US radio programme earlier this year.
"I haven't formally endorsed him, but I do support his candidacy," Mr Duke said in February.
He used to lead Klu Klux Khan, an American white supremacist organisation responsible for publicly hanging numerous black people and supporting racial segregation.
Speaking during an interview published on PremierChristianity.com, Mr Claiborne said: "Right after David Duke, the former head of the KKK, endorsed Trump, I said it must make us question whether Christians should be aligned with the same candidate that the KKK has endorsed!"
In suggesting that Mr Trump could be picking up votes from white supremecists, Mr Claiborne said, "We have a racial justice awakening happening in our country.
"Black lives matter... So the support of Donald Trump is evidence of some reactionary [backlash]. White supremacy rises up a lot of times in reaction to that."
He also criticised Mr Trump for not speaking about Jesus when he visited America's largest Christian university.
"When Donald Trump spoke at Liberty he didn't say much about Jesus. We need to say a lot more about Jesus. Jesus actually needs to be the centre of our Christianity.
"A lot of evangelical Christianity has ironically lost track of Jesus. The more you read the words of Jesus, you find yourself really baffled by what evangelicals have become known for!'
"There's a young generation that could care less about labels that says 'we love Jesus and we want to change the world'. 80% of millennial evangelicals are against the death penalty - because they can't reconcile it with Jesus."
