Today may be the most important day of Sen. Orrin Hatch’s (R) bid for a seventh term. The Hatch campaign, fending off state GOP convention challenges from conservative opponents, has recruited and trained thousands of people to run as delegates for Hatch in tonight’s local caucuses being held around the state.

The 4,000 delegates elected will go on to vote at the April 21 convention, where a nominee can emerge with 60 percent of the vote. If no one cracks that mark, the top two finishers go on to a June 26 primary.

“The campaign has been working toward caucus night for over a year,” Hatch spokeswoman Evelyn Call said. “With dozens of field staff, hundreds of thousands of phone calls and countless man hours we have been able to bring the Senator’s message to all corners of the state.”

Hatch is facing his most difficult campaign since he was first elected in 1976 with an endorsement from Ronald Reagan, who is still quoted on Hatch’s campaign website. Hatch, who turns 78 next week, said Tuesday that his seventh term would be his final term.

Scads of Republicans are hoping to replicate the 2010 convention defeat of then-Sen. Bob Bennett, most notably state Rep. Chris Herrod and former state Sen. Dan Liljenquist, who may be the favorite to unseat Hatch.

“There is a whole new generation of people involved in politics in Utah, who Orrin Hatch has been there almost their entire lives,” Liljenquist told Roll Call just before walking into his 92nd event since joining the race in January. “And they’re ready for some change.”

Liljenquist and Herrod are hardly Hatch’s only opponents, as conservative groups such as FreedomWorks have actively worked to defeat him. The D.C.-based organization has spent $575,000 in independent expenditures on the race this year alone.

FreedomWorks Vice President of Political and Grassroots Campaigns Russ Walker said in a statement the race “will be won or lost in the caucuses” tonight. He said his group “will continue to work with like-minded limited government conservatives in Utah until a true small government constitutional conservative takes Hatch’s place on the Hill.”

Hatch has also received support from outside groups, including the Strong Utah political action committee and nonprofit Freedom Path.

It will likely take several days for the Hatch campaign to decipher where he stands following tonight’s contests. Then on to the convention he goes.