PIKEVILLE, Ky. — Most any other year, this state’s open Senate seat would be Trey Grayson’s.

At 37, Mr. Grayson has spent more than a decade working his way up through the state’s Republican Party, courting officials and solidly winning re-election as secretary of state three years ago even as voters turned out a Republican governor. He has a powerful backer in Mitch McConnell, Kentucky’s senior senator and the Senate’s highest ranking Republican. He graduated from Harvard, but his roots here go five generations deep. He even looks the part: monogrammed cuffs, rep tie and a not-too-stylishly-cut black suit over his 6-foot-5 frame.

This, however, is no ordinary year.

And in Kentucky, the Tea Party movement, with the voter discontent it has captured, has found its purest standard bearer in Rand Paul, who is challenging Mr. Grayson for the Republican nomination. An ophthalmologist, Dr. Paul is the son of Representative Ron Paul of Texas, the 2008 Republican presidential candidate whose libertarian backers often take credit for being the germ of the Tea Party.

While there are candidates backed by the Tea Party in other states, none is so much a product of it, with the name recognition and the fund-raising prowess (through his father’s network). And the proportions of Kentucky’s voter registration make it impossible for any Republican to win a general election without Democratic support, so if Dr. Paul wins the primary on May 18, as polls suggest he will, the Tea Party will have to prove its appeal beyond the Republican right.

So far, the Tea Party’s big victories have been about what it is against — electing Scott Brown in Massachusetts had less to do with the candidate than with blocking health care legislation. Kentucky offers the chance to show what the movement is for, and if voters will go along with it.