(REUTERS) — Seeking one last term, Republican U.S. Senator Orrin Hatch is facing what may prove to be the toughest re-election of his 36-year tenure in Thursday’s Utah Republican caucus against two popular younger Tea Party-backed candidates.

Conservative and heavily Republican Utah last elected a Democrat to the U.S. Senate more than four decades ago, so the Republican nominee is usually considered the presumptive winner of the general election in November.

For a senior stalwart of the Republican mainstream like Hatch, the ranking Republican on the tax-writing Senate Finance Committee, the Senate seat has long been regarded as his to lose. He was first elected in 1976 and turns 78 next week.

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