Embattled Rep. Scott DesJarlais (R-Tenn.) led his primary challenger by just 35 votes out of more than 75,000 cast early Friday, leaving the race in doubt nearly 12 hours after polls closed on Thursday.
With all precincts reporting, DesJarlais led state Sen. Jim Tracy 34,787 to 34,752. Five other candidates lagged well behind. The Associated Press has yet to call the race in favor of either candidate.
DesJarlais, a physician, was set back by 2012 revelations that he had extramarital affairs with patients and encouraged his then-wife to get abortions, despite campaigning as an antiabortion conservative.
Tracy's campaign said in a statement that "there are ballots left be counted," an apparent reference to outstanding provisional and absentee ballots.
According to the Nashville Tennessean, Tracy declared victory at one point Thursday evening.
State law on recounts is vague. It allows for a court or election officials to order a recount in the case of a tie, indications of fraud or malfunction, or for other reasons that would make one necessary.
The winner will face Democratic nominee Lenda Sherrell in November and will be heavily favored to win, given the district's heavy rightward tilt.