A California man named William Johnson has placed a robocall in the state identifying himself as a "farmer and a white nationalist" and alleging that McMullin "has two mommies." McMullin grew up with both a father and a mother, but his parents have since divorced and his mother is now in a lesbian relationship.
Johnson also alleges -- without evidence -- that McMullin is gay because he is currently single.
"Don't vote for Evan McMullin. Vote for Donald Trump. He will respect all women and be a president we can all be proud of," the call concludes.
The Trump campaign quickly rebuked Johnson.
"We strongly condemn this rhetoric and these activities of which we have no knowledge," Trump spokesman Hope Hicks said Monday.
The campaign distanced itself far more quickly than it has some other white nationalists in the past, including when Trump repeatedly demurred to CNN's Jake Tapper about David Duke's support, before finally condemning him.
In an interview with Tapper on "The Lead" Tuesday, McMullin said he wasn't surprised by the robocall, saying it "is exactly the narrative and the approach the Donald Trump campaign has had."
"Trump supporters have attacked me because of my faith, they've attacked my service, we've even received some death threats from these white supremacists, even recently, overnight," McMullin continued. "They've attacked my family, but, you know, they've attacked so many other Americans, too. Donald Trump himself has bragged about sexually assaulting women and attacked people for the color of their skin and their faith. I mean, this is the Republican nominee and none of this should surprise any of us."
White supremacists have found unusual comfort in Trump, who has stoked nationalist sentiment among supporters and launched some racially based attacks during the campaign, from proposing a ban on Muslim immigration and accusing Mexican immigrants of being criminals and "rapists."
The call has barely any money behind it -- just $2,000, Johnson said, and will go to 193,000 homes between Monday and Wednesday evening. But it is a reflection of the growing threat posed by McMullin, who has lead Trump in some polls in the ruby-red state.
UPDATE: This story has been updated to include McMullin's response.