The Kentucky Senate Democratic primary race to determine who takes on Senate Majority Leader Mitch McConnell in November is too close to call, NBC News projects.

Amy McGrath, a retired Marine lieutenant colonel, had a slight edge in a tougher-than-expected challenge from state Rep. Charles Booker. With 10 percent of the vote in by Wednesday morning, McGrath led Booker, 44 percent to 39.6 percent, a margin of just over 2,000 votes. But that tally includes only ones cast in person at the polls Tuesday; none of the substantial number of mail-in ballots that could determine the outcome have been counted and will not be for days.

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