“You can’t help who admires you, but when white supremacists start endorsing you for president, you ought to start asking why,” said Richard Cohen, the president of the Southern Poverty Law Center, which tracks white-power groups…

Mr. Trump’s support among white supremacists has been building from the day he announced his candidacy, when he characterized Mexican immigrants as “rapists.”

Since then, Mr. Trump — or “the glorious leader,” as one white-power writer is calling him — has only grown more popular with that constituency, which cheered his proposal to ban all Muslim immigration and his since-debunked claim to have seen “thousands and thousands of Muslims” celebrating the terrorist attacks of Sept. 11, 2001, in New Jersey…

Mr. Trump’s failure to distance himself more sharply from white-power adherents has been minutely observed in online discussion forums…

“The march to victory will not be won by Donald Trump in 2016, but this could be the steppingstone we need to then radicalize millions of White working and middle class families to the call to truly begin a struggle for Faith, family and folk,” Matthew Heimbach, co-founder of the Traditionalist Youth Network, wrote on the group’s website in October.