It’s primary election day in Kentucky, the day the state’s Republicans decide whether they will send a long-time Senate minority leader or a Tea Party freshman to face off with Democratic challenger Alison Lundergan Grimes.

Mitch McConnell is the Senate minority leader and won his seat in 1984. His challenger is Matt Bevin, a businessman and Tea Party candidate who told the New York Times he would make history by being the first primary candidate to beat an incumbent with a congressional leadership position.

However, the endorsement from Rand Paul, Kentucky’s junior Republican senator and a Tea Party hero, went to McConnell. Bevin, despite a lot of attack ads and some time on talk radio, will probably lose. He was twenty points down in polls a week before the election, according to Politico.

The election is among the most closely watched primaries and has national implications. McConnell has told voters as much. He has urged Kentuckians to get past the establishment frustrations that have pushed his Tea Party opponent forward and look to the finish.

“If the Democrats win in either Kentucky or Georgia, it will be next to impossible for Republicans to take the Senate in 2014,” Ford O’Connell, a Republican Party strategist, told the Washington Times. “That is the bottom line.”

Spending by candidates has reflected the relatively unusual urgency of Kentucky’s primaries. Republicans have spent $26 million; Democrats have used another $8 million, according to Talking Points Memo. And the Center for Responsive Politics says McConnell has another $10.1 million on hand from fundraising.

McConnell will almost certainly defeat Bevin tonight. But after that the Kentucky Senate race could become one of the most interesting—and challenging—of 2014.