MAPLETON — Chris Cannon was in Washington, D.C., working in Congress when one of his cows gave birth to a calf in the snow on his family's 18-acre spread.

The calf nearly froze to death, but Cannon's two young sons, Matt and John, came to its rescue. The boys wrapped it in their mother's heating pads and coaxed it back to health.

Cannon decided two things when he heard the story. One, the family needed to cut its herd because he was gone too often and, two, he would come home from Congress when he felt his influence begin to wane.

His theory faces a test Tuesday when Cannon will try to fend off challenger Matt Throckmorton in the Republican primary.

These aren't uncharted waters for Cannon, but they are unfamiliar.

Until this year, the four-term congressman had never won less than 61 percent of the votes at the GOP convention, and it had been six years since he faced a primary challenge.

He still topped Throckmorton, 58 percent to 42, at this spring's Republican convention, but national groups opposed to Cannon's proposed immigration bills saw the slight slippage — which resulted in a primary because Cannon didn't break 60 percent — as a sign their issue has traction, and Throckmorton continues to pound on Cannon over immigration.

One of Cannon's more controversial bills would provide temporary legal status to undocumented immigrants who agree to register with the government and work in agricultural jobs. He says more than 60 senators are lined up in support of the bill, which also has President Bush's tacit support.

That doesn't make it a slam dunk, however.

Cannon has been attacked on billboards and in radio ads and e-mail campaigns paid for by national lobbying groups. He bristles at the broadsides, which paint him as soft on borders.

Both sides want to reform American immigration policy. Cannon wants to streamline documentation and employment opportunities. His opponents seek tougher borders and tough stands on illegal activity.

With that backdrop, if the agricultural jobs (AgJOBS) bill passes this fall, it could provide a boost for a second, larger immigration reform bill with Cannon's name on it.

"When my influence stops rising, when I'm not able to do more, I'll leave" Congress, he says. If those bills pass, "my influence will rise."

It's no surprise Cannon is in the middle of controversy or is the center of an ambitious project.

Cannon is an excitable man smitten with big ideas.