The polls have opened, but Roy Moore's race to the Alabama Senate remains too close to call.
The Republican candidate is neck-and-neck with Democrat rival Doug Jones.
Moore originally had the lead before a series of allegations over sexual misconduct with school girls.
Moore has denied the accusations.
He continues to have the backing of Donald Trump, but has lost the support of the Republican establishment.
1News US correspondent Rebecca Wright told Rachel Smalley the allegations could keep many Republican voters away.
"If Republicans do decide to stay home, it will be a humiliation not only for Roy Moore but for the President who has endorsed Moore."
LISTEN TO REBECCA WRIGHT TALK WITH RACHEL SMALLEY ABOVE
Take your Radio, Podcasts and Music with you