The race in Michigan's 6th congressional district between incumbent Republican Congressman Fred Upton and Democrat Paul Clements has become surprisingly close—with Clements trailing the chairman of the powerful House Committee on Energy and Commerce by just a few points.

But until a few days ago, almost no one outside of the district was watching or involved in the race.

"It is now possible, if not likely, that this could be one of the biggest surprises coming out of the Midwestern congressional races," said Barry Rabe, an expert on the politics of climate change at the University of Michigan.

Upton was largely considered unbeatable thanks to his fourteen-term incumbency and ties to the fossil fuel industry, which has kept his campaign coffers full year after year. National environmental and political organizations like the League of Conservation Voters, the NRDC Action Fund and the Democratic Congressional Campaign Committee focused their efforts elsewhere. Even pollsters weren't tracking the race, at least not publicly.

Only two small super PACs got involved to help boost Clements, a political science professor at Western Michigan University. One was Climate Hawks Vote, which works to get climate-conscious candidates into office. The other was MaydayPAC, a crowdfunded group that strives to elect officials who support campaign finance reform.

"There should have been more groups involved, especially more environmental groups, considering this is the chair of the House energy committee," said RL Miller, founder of Climate Hawks Vote. "But they all saw it as a long shot. I got involved partly to send a message, but also because I didn't think it was quite as long a shot."

Climate Hawks Vote runs on a shoestring budget, opting for phone banking and door-to-door campaigning instead of running more expensive print and broadcast ads. The super PAC has had someone on the ground in Michigan since the beginning of September. Its strategy has been to boast about Clements' pro-climate action position while drawing attention to Upton's ties to the oil industry.

Upton has represented the district since 1987. Once a moderate on environmental issues, he started pushing a pro-fossil fuel agenda when the Tea Party movement took hold in 2010, including challenging the Environmental Protection Agency's ability to regulate greenhouse gas emissions. Upton's campaign website names him "a champion of the Keystone XL pipeline," a project that could send 800,000 barrels of carbon-heavy crude oil from Alberta to refineries in Texas. He is frequently one of the top Congressional recipients of oil, gas, and coal campaign contributions. He's received $222,650 from oil and gas companies so far this election season, according to the campaign finance website OpenSecrets.org.

But residents in Michigan's 6th congressional district seem to be losing patience with Upton's anti-environmental activities. The region has a long legacy of industrial pollution. It is also home to several pipelines carrying fossil fuels from Canada to Texas, and is the site of the largest inland oil pipeline spill in U.S. history, the 1-million barrel tar sands crude leak along the Kalamazoo River in 2010.

In September, a natural gas pipeline leak within the district displaced 500 people and gave pro-Clements campaigners another example in their fight.

A poll released last week by the Clements campaign shows that Upton's support has declined 10 points in a month, dropping from 57 percent to 47 percent. The race now stands at 47-43, with Upton's 4-point lead within the survey's 5-point margin of error. The Cook Political Report, a well-respected election forecast group, lowered Upton's likelihood of winning from "solid" to "likely" last week.

Political donors from both sides of the aisle have swept in to make last minute campaign contributions to sway undecided voters. Republicans are projected to increase their majority in the House. Even if Upton wins, a close race portends an opportunity for Democrats to prevail in the district in 2016.

The American Future Fund, a group largely funded by Charles and David Koch, made a new $300,000 ad buy last week, according to Politico.

MaydayPAC, which already committed $1.5 million to defeating Upton, announced last week it would spend another $650,000 in the race's final days. Betsy Taylor, president of Breakthrough Strategies & Solutions and an adviser to climate donors, and Marc Weiss, a producer and climate activist, have urged their informal network of climate-conscious donors to give money to the Clements campaign.

"We had not targeted this race before because the general wisdom was that Upton is untouchable," Taylor told InsideClimate News. "But Clements is running a strong challenge and at the very least, he is forcing Big Oil super PACs to unexpectedly redirect funds to Upton and away from the tight Senate races."