A white nationalist group, the American National Super PAC, has paid for a massive robocall campaign to blanket Iowa with pro-Trump calls. The group has called Trump its "great white hope" (warning, like to white supremacist site) and is paying for a 50 second call with an absolute white supremacist script to go out to Iowa voters:
The American National Super PAC makes this call to support Donald Trump.
‘My name is Reverend Ronald Tan, host of the Christian radio talk show program For God and Country. First Corinthians states: God chose the foolish things of this world to shame the wise and God chose the weak things of this world to shame the strong. For the Iowa caucuses, please support Donald Trump. He is courageous and he speaks his mind. God Bless.’
‘I’m Jared Taylor with American Renaissance. I urge you to vote for Donald Trump because he is the one candidate who points out that we should accept immigrants who are good for America. We don’t need Muslims. We need smart, well-educated white people who will assimilate to our culture. Vote Trump.’
‘I am William Johnson, a farmer and a white nationalist. Support Donald Trump. I paid for this through the super PAC. [Telephone] (213) 718-3908. This call is not authorized by Donald Trump.'”
I'm not really one to hold candidates responsible for their supporters. I don't hold Rubio responsible for the establishment kleptocrats who support him, I don't hold Cruz responsible for everything Steve King says, and I don't hold Trump responsible for the nuts who support him.
That having been said, this does have the potential to do some damage to Trump's standing in Iowa. First, people hate getting robocalls and they tend to negatively view any candidate who supports them. Second, anyone who gets to the part where the redneck explains that we need "smart white people" in this country is probably going to hang up in disgust before the disclaimer, and some non-trivial number of them will assume that Trump is behind this.
Third, any other candidate would defuse this controversy by issuing a blanket denial of their association with the group or their ideals, but the Trump campaign instead is going with "no comment." We'll see how well that plays out in the end.