CHEYENNE, Wyo. (AP) — A little-known Democrat faces overwhelming odds Tuesday against John Barrasso, Wyoming's long-serving and high-ranking Republican U.S. senator.

Scott Morrow, a retired postal union official from Laramie, is challenging Barrasso, who has been a well-known fixture in the state for decades and has served in the Senate since 2007.

An orthopedic surgeon, Barrasso was a state lawmaker from Casper before he was appointed to the Senate seat following the death of Republican Sen. Craig Thomas. Before that, Barrasso was known throughout the state for a regular, local TV news segment in which he discussed medical issues.

Barrasso has been an outspoken critic of the Biden administration’s policies on immigration, fossil fuel development and air pollution regulations.

And he has been a firm supporter of Donald Trump, avoiding the ire of the former president that undid the political career of former Wyoming U.S. Rep. Liz Cheney two years ago.

Barrasso has won his three Senate races so far by wide margins.

Over 17 years in the Senate, he has risen to chair of the Senate Republican Conference, the third-ranking GOP position in the chamber, and is the ranking member of the Senate Energy and Natural Resources Committee.

Morrow campaigned as an advocate of labor unions and abortion rights.