The Montana Supreme Court on Tuesday affirmed a lower court ruling that allowed the state’s Green Party Senate candidate to remain on the ballot in November, a blow to Democrats’ efforts to prevent what they expect could be a spoiler in the close race between incumbent Sen. Jon Tester (D) and his Republican challenger, Tim Sheehy.

The Montana Democratic Party filed a lawsuit in late August contesting the nomination of Green Party candidate Robert Barb, who placed second in the state’s Green Party primary but replaced the top vote-getter after the winner dropped out of the race.

The Green Party submitted the necessary paperwork to the secretary of state, Christi Jacobsen, declaring Barb the replacement candidate for the Green Party, but the state Democratic Party argued that the Green Party did not follow proper protocol and filed a lawsuit against the secretary of state and the state of Montana to block Barb’s name from appearing on the ballot.

In its ruling Tuesday, the state’s Supreme Court determined the Democrats “failed to demonstrate that it is likely that the Montana Green Party violated its party ‘rules’ when its state central committee appointed Barb to fill the vacancy.”

The court agreed with the defendant’s argument pointing out that the Green Party bylaws “are silent” on how the party should replace a candidate who drops out, making Democrats' "allegation that the Montana Green Party failed to appoint Barb in accordance with its bylaws ... merely speculative.”

The ruling affirms a lower court ruling denying the Montana Democratic Party's request for injunctive relief, arguing it did not follow the “express and exclusive statutory process for contesting nominations” and was therefore unlikely to succeed in making its case.

The Montana Supreme Court disagreed with the lower court’s reasoning but ultimately arrived at the same conclusion.

Montana Democratic Party Chair Robyn Driscoll called the ruling "disappointing" and took aim at Barb and the state’s Republican Party in an emailed statement Wednesday. 

“While today’s ruling is disappointing, the Montana Democratic Party will continue to make sure that voters know the truth about Robert Barb: He is a well-known Republican who shares right-wing conspiracy theories and believes climate change is a ‘B.S. fake narrative,’” Driscoll said in the statement.

“We strongly condemn the Montana Republican Party’s blatant manipulation of voters and troubling refusal to follow Montana election law, and we will continue to share the truth from now until Election Day,” Driscoll added.

The secretary of state said she was pleased with the outcome.

"I'm pleased that the Supreme Court unanimously rejected this hail mary attempt to undermine Montana election law," Jacobsen said in an emailed statement. "From the start, this lawsuit was a baseless political game from Washington elites that showed complete disrespect for Montana and our election officials."

The Hill has contacted the Green Party for a response.

Tester is fighting to retain his Senate seat in the deep-red state that will prove critical in determining control of the upper chamber.

The Cook Political Report recently made a "major shift," moving the Montana Senate race from “Toss Up,” to “Lean Republican,” as Republicans increasingly like their odds of defeating the incumbent in the battleground state.

Several recent polls have shown Sheehy, a businessman, leading Tester by a few points, within the margin of error but short of what Democrats would like.

An AARP poll from last month showed Sheehy leading Tester by 6 points, while an internal poll from the Senate Republicans’ campaign arm had Sheehy up by 4 points.

Story updated at 4:47 p.m. ET