Twenty-six Democratic candidates have been invited to the forum, as have President Trump and William Weld, a former Massachusetts governor who is challenging Trump for the Republican presidential nomination.

+3 South Sioux City's Frank LaMere remembered as Native American voice for the voiceless SOUTH SIOUX CITY -- Frank LaMere, who spent decades of his life fighting for various causes to help his fellow Native Americans, lost his own …

"I'll be honest with you, I think most of the candidates are going to be here, because this is the one time they'll get to speak to six million Native Americans in the United States," said Matt Samp, a spokesman for Four Directions. "We have soft commitments from, I'd say nine of them."

Samp said the official lineup won't be released until July 19.

Over two nights, candidates will take questions from panels of elected tribal officials, tribal members and Native American youth. Mark Trahant, a member of the Shoshone-Bannock Tribe and the editor of Indian Country Today, a Washington, D.C.-based publication, will moderate the forum.

Marcella LeBeau, a 99-year-old member of the Cheyenne River Sioux Tribe, a World War II veteran of the U.S. Army Nurse Corps and a recipient of the French Legion of Honor, will be a featured guest.