Who senators choose, and whether Trump ultimately endorses a candidate in the final hours, could set the tone for Trump’s attempts to assert control over the legislative branch.

In the first seriously contested Senate Republican leadership election in decades, three senators are vying to replace longtime GOP leader Mitch McConnell when he steps down from the post at the beginning of next year.

Following the election, Republicans will control the Senate with a 53 to 47 majority, but one question remains -- who will become the new Senate majority leader? Outgoing leader Mitch McConnell will remain in Congress but will step aside as the longest serving party leader in history.

He's a wealthy Floridian who has taken aim at fellow Republicans while pushing to consolidate power in Washington, and his name is not Donald Trump.