Tester’s campaign contends low natural-gas prices are forcing PPL Montana to mothball the Corette plant.
Aaron Murphy, a spokesman for Tester's campaign, noted PPL Montana shut down Corette for more than three months this year due to low demand.
“Jon Tester has a powerful record of supporting responsible coal development, and Dennis Rehberg is lying when he tries to blame Jon for the closure of Corette,” Murphy told The Hill in a statement.
Montana was Inhofe's first stop on a three-state swing in which he will stump for candidates who want to repeal environmental rules the Oklahoman opposes. The current ranking member of the Senate Committee on Environment and Public Works, Inhofe is in line to take the chair if Republicans control the Senate.
Next week, Inhofe will become one of just a handful of GOP senators to publicly campaign for Missouri Senate candidate Rep. Todd Akin (R) since his controversial “legitimate rape” comments, in which he suggested pregnancies were unlikely to occur after a rape.
In the House, Akin consistently voted against imposing various environmental and air-quality rules. But the rape remarks sent Akin’s campaign into a tailspin, as he now trails Sen. Claire McCaskill (D) in most polls.
Inhofe also plans to stump for Ohio GOP Senate candidate Josh Mandel. Mandel, the state's treasurer, trails Sen. Sherrod Brown (D).
Inhofe is backing the candidates to bring GOP colleagues to the Senate to achieve one of his key legislative aims — curbing the administration's environmental and air rules.
Inhofe sponsored a bill that would have prevented the administration from implementing the air pollution rules. Tester voted against the measure, which failed 46-53 in June.
"Missouri, Montana and Ohio are three of the largest coal states of all the states," Inhofe said, according to KTVQ in Billings. "In each one of these states, you have a Democrat incumbent senator who has voted to kill coal."
Rehberg has hit Tester several times on the campaign trail and in advertisements for casting that vote. Inhofe emphasized Monday that Rehberg could help swing a similar vote next Congress if he wins the Senate seat.
Tester’s support for the rules has helped garner backing from environmental group the League of Conservation Voters (LCV). The group has spent $2 million backing Tester, with his stance on the air pollution chief among the reasons for LCV’s support.
RealClearPolitics, a website that aggregates polling data, shows Tester and Rehberg in a dead heat. It gives Rehberg a 0.3-percentage-point lead.
— This story was updated at 10:41 a.m.