U.S. Rep. John Curtis is the favorite to fill Mitt Romney's vacant Senate seat in Utah

PROVO, Utah (AP) — Utah voters face a decision about whether a Republican representative or his lesser-known Democratic opponent will succeed Mitt Romney in the US Senate.

U.S. Rep. John Curtisthe longest-serving member of Utah's House delegation, is considered the heavy favorite to win in a deep red state that hasn't elected a Democrat to the Senate since 1970. He is considered a moderate Republican in the spirit of Romney, but promises to leave the Senate for his own brand of conservatism if elected.

Curtis faces Democrat Caroline Gleich, a mountaineer and environmental activist from Park City who has tried to convince voters that her opponent is not as moderate as he seems.

Both are vying to succeed one of Washington's most prominent centrists and outspoken critics of former President Donald Trump.

The candidates often argued about it different approaches to climate changea top topic for both.

Curtis, 64, is the founder of the Conservative Climate Caucus on Capitol Hill. The coalition presents GOP alternatives to Democrats' climate policies that Curtis says are aimed at reducing emissions without endangering American jobs or economic principles.

During his seven years in Congress, Curtis developed a reputation for pushing back against party leaders like Trump who have falsely claimed that climate change was a hoax.

Gleich, 38, has accused Curtis of aligning himself with the fossil fuel industry and criticized him for voting against Democratic proposals that they say could have better protected public lands, air and water.

Moderate Republicans tend to prevail in statewide elections in Utah, as evidenced by Curtis' victory over a Trump-backed mayor in June GOP primary.

Members of The Church of Jesus Christ of Latter-day Saints, who make up about half of the state's 3.4 million residents, have been a reliable Republican voting bloc for decades. But many were hesitant to embrace Trump and his allies, saying the former president's brash style and comments about immigrants and refugees contradicted their religious beliefs.

Polling stations nationwide open at 7 a.m. and close at 8 p.m