Because the contest is a special election to finish McCain’s term, the winner could be sworn in as soon as the results are officially certified. Other winners in the November election won’t take office until January.

Trump has pledged to nominate a replacement for Justice Ruth Bader Ginsburg, a liberal icon who died Friday, and Senate Majority Leader Mitch McConnell vowed that Trump’s nominee “will receive a vote on the floor of the United States Senate.”

If Kelly wins, the timing when he formally takes office could be crucial in determining who replaces Ginsburg. It could eliminate a Republican vote in favor of Trump’s nominee — the GOP currently has 53 seats in the 100-member chamber — or require McConnell to speed up the nomination process.