Hillary Clinton and Donald Trump's ugly and acrimonious battle for the White House is barreling toward the end, with the candidates taking the debate stage Wednesday night for one final primetime showdown.

For Trump, the debate is perhaps his last opportunity to turn around a race that appears to be slipping away from him. His predatory comments about women and a flood of sexual assault accusations have deepened his unpopularity with women and limited his pathways to victory. His supporters remain intensely loyal, but there are few signs he's attracting the new backers he desperately needs.

Clinton takes the stage facing challenges of her own. While the electoral map currently leans in her favor, the Democrat is facing a new round of questions about her authenticity and trustworthiness, concerns that have trailed her throughout the campaign. The hacking of her top campaign adviser's emails revealed a candidate that is averse to apologizing, can strike a different tone in private than in public, and makes some decisions only after painstaking political deliberations.

The last in a trio of presidential debates, Wednesday's contest in Las Vegas comes just under three weeks from Election Day and with early voting already underway in more than 30 states. At least 2.1 million voters have cast ballots already.