South Dakota Sen. Mike Rounds easily fended off Democratic challenger Dan Ahlers.<br />Polls closed at 8 p.m. local time/9 p.m. ET.<br />Business Insider called the race in Rounds' favor.<br />Rounds won his Senate seat in 2014 after defeating his Democratic opponent by 21 percentage points.<br />South Dakota overwhelmingly voted for President Donald Trump in the 2016 presidential election.
