Who Donald Trump and Hillary Clinton Invited to Tonight's Debate

Obama's half-brother is a Trump guest, and Clinton has invited Mark Cuban.

The Republican nominee invited Malik Obama, the president's half-brother, to sit in the audience at tonight's third and final 2016 presidential debate, at the University of Nevada in Las Vegas.

White House press secretary Josh Earnest said he does not understand the intent behind the Trump campaign's invitation to Obama.

"I don't anticipate that the president has spent a lot of time considering whether or not [Obama] should attend the debate," Earnest said during today's White House press briefing. "I have to admit I really don't know exactly what the intent is of this invitation."

Trump has invited Leslie Millwee, a woman whose decades-old sexual assault allegations against Bill Clinton were made public for the first time today on the conservative news website Breitbart.

Trump isn't the only one taking some big names to Las Vegas.

Cuban was spotted in the spin room ahead of the debate, as well as Meg Whitman, an executive at Hewlett Packard Enterprise.

It was not clear whether Bill Clinton will be joining his daughter in the debate hall.

Some of Hillary Clinton's other guests have personal connections to policy initiatives and issues that have come up in the campaign, including immigration and education programs for undocumented residents.

One such guest is 11-year-old Karla Ortiz, who lives in Nevada and has been featured in Clinton's campaign before. Most notably, she appeared onstage during the Democratic National Convention and is featured in one of Clinton's campaign ads. Karla was born in the United States but because her parents are undocumented, she reportedly fears that they will be deported.

ABC News' John Parkinson and John Santucci contributed to this report.