When the Democrats threw their weight behind Katie McGinty in the race for Pennsylvania's U.S. Senate seat, they signaled this race is one of their best hopes for climate action in a new Congress.

The party also was marking the limits of its green ambitions.

In a race that could be key to deciding control of the Senate, McGinty is seeking her first elective office after a career steeped in environmental policymaking. Starting as a Senate aide to Al Gore in the 1980s, she later served as top White House environmental adviser in Bill Clinton's administration, then returned to her home state to head Pennsylvania's environmental agency.

"With her background, she can be a strong voice in the Senate on environmental issues from day one," said Joe Bonfiglio, vice president of EDF Action, the political arm of the Environmental Defense Fund, which has endorsed McGinty.

McGinty would be part of a Senate majority if the Democrats can gain at least four or five seats out of the eight competitive races, with the president's party casting the deciding vote in a tie. The GOP now holds a 54-44 majority. (It will be more difficult for Democrats to capture the 30 seats necessary to take control of the House.)

But McGinty is locked in dead heat with a well-funded Republican incumbent, Sen. Pat Toomey, in a traditional coal state that has become an epicenter of the fracking boom. It's also an electoral swing state, and the outcome of the Senate race could depend on the coattail effect of the presidential vote. That means McGinty's fortunes are tied to Hillary Clinton's.

Accordingly, their climate and energy policies are right in line.

Like Clinton, McGinty embraces the science on global warming, its human causes, and the peril for the planet. She lambastes what she calls the "Trump-Toomey ticket" for climate denial, and pledges to work in the Senate for "common-sense climate protections with investments in energy efficiency and clean energy." But also like Clinton, McGinty stops short of calling for any firm goals to reduce U.S. oil and gas production. Don't expect her to utter the phrase, "Leave it in the ground."

McGinty, who has received $5 million in support so far from environmental groups and coalitions, backs an "all-of-the-above" energy strategy, similar to the one adhered to by President Obama and that guides Clinton. This is despite science showing that much of the world's remaining fossil fuel reserves—especially coal—need to stay in the ground and that using natural gas as a bridge strategy poses risks.

The League of Conservation Voters (LCV) and EDF Action Fund endorsed McGinty in the Democratic primary, backing her over two opponents who supported a fracking moratorium. "We endorsed her enthusiastically in the primary because we think she has spent her career working to protect the environment and public health," said Tiernan Sittenfeld, LCV's senior vice president for government affairs. "She's not just going to be a reliable vote, but a true champion in every sense of the word, and someone who is going to be effective, and really rise to one of the defining challenges of our time, combating the climate crisis."

The green groups emphasize McGinty's statements supporting more regulation of fracking to explain why they support her. They made clear that they believed she was more likely to beat Toomey in the general election. The national Democratic Party apparently agreed, endorsing McGinty in the primary and investing $17.7 million to elect her—more than it has spent on any other Senate candidate.

A Deep History in Policy

McGinty's most recent government post was as chief of staff to Pennsylvania Gov. Tom Wolf, but her pedigree is as an environmental policymaker. Fresh out of Columbia Law School in 1988, with an undergraduate degree in chemistry, she joined Gore's Senate staff as a fellow and over time became his senior environmental aide.

She played a key role in shaping Congress' 1990 expansion of the Clean Air Act, which helped set the stage for strict regulation of fossil fuel power plants, including their carbon emissions.

When Gore became vice president, McGinty, too, moved to the executive branch—and at age 29 was named the first female chair of the White House Council on Environmental Quality. In that post, she pressed President Clinton to establish the 1.8-million-acre Grand Staircase-Escalante National Monument in Utah in 1996. That put a coal seam then worth an estimated $1 trillion out of the reach of the mining industry.

But the environmental achievement that McGinty talks about most on the campaign trail was her work that led to passage of Pennsylvania's 2004 law requiring 18 percent of the state's energy to come from alternative sources by 2021. "We went from being nowhere to literally being one of the top states in the country in wind energy, in solar energy, in energy efficiency," McGinty said in an interview with Temple University's radio station. "That's why people who care about the environment are for me. But it's also people who care about jobs are for me, because I brought 3,000 new jobs in that clean energy space here."

Money Talks

Pennsylvania's has become the most expensive Congressional race this year, with both sides seeing it as the battle line for a Senate majority. Toomey, a former Wall Street banker and regulatory foe, has raised $23 million for his campaign—more than three times McGinty's $7 million.

Then, there are the enormous sums invested by Super PACs and advocacy organizations. McGinty has edged Toomey in that category, with the Democratic party, environmental groups and others pouring $36 million into advertising and canvassing. On Toomey's side, $28 million has been spent, led by the libertarian fossil fuel industry billionaire Koch brothers, the U.S. Chamber of Commerce and wealthy donors in the finance industries. He has been endorsed by billionaire Michael Bloomberg, the former mayor of New York, despite Bloomberg's emphatic support of Clinton in the presidential race.

The money has produced a sea of attack ads via TV, direct mail and the internet.

"The reason for the outside money is simple," said G. Terry Madonna, political scientist and pollster at at Franklin & Marshall College in Lancaster Pennsylvania. "It's a race that could be won by either candidate."

Toomey only won his Senate seat by two percentage points in 2010. "Republicans think Toomey's staunch conservatism is likely to defeat him," Madonna said, in a state that has voted Democratic in the past six presidential elections.

Before Toomey became senator, he led a movement to push Congress to the right. He was president of the advocacy group, the Club for Growth, which campaigns to unseat moderate incumbent Republicans and replace them with hard-liners. Its funders include Koch groups and wealthy financiers.

McGinty's campaign and her supporters have aimed to tap into Pennsylvania populism by hammering Toomey on his ties to Wall Street and fossil fuel interests. "Big oil polluters. They have a friend in Pennsylvania," says one of the LCV ads attacking Toomey.

Fracking: Pennsylvania Politics' Third Rail

But energy is a touchy subject in Pennsylvania, which is now the No. 2 natural gas producer in the U.S. behind Texas, with an eight-fold surge in production in just five years. Oil and gas industry employment in Pennsylvania tripled to more than 33,000 in seven years. It has brought hope for jobs in an area hit hardest by the decline in heavy manufacturing since the 1970s. And although new drilling has fallen dramatically due to low gas prices, the industry promises more jobs as it establishes new ways to market its product: Shell building a giant petrochemical complex near Pittsburgh, tens of thousands of miles of pipeline being laid, and plans for an export terminal in Philadelphia.

The industrialization the industry is bringing to the state's beloved mountains and forests, however, concerns many in the state. They worry about air and water pollution and health impacts. LCV polling also shows 71 percent of Pennsylvanians view climate change as a serious problem, but there is not as strong a consensus on fracking's contribution to the problem. The state's reported carbon dioxide emissions from fossil fuel consumption have fallen 11 percent during the fracking boom, because cheaper natural gas has displaced more carbon-intensive coal as the source of electricity.

Reflecting this mix of economic and environmental concerns, polling shows voters generally support the shale gas industry, though they would like to see it taxed, regulated and kept out of state forests and parks. "Overall, voters want it, but they want it environmentally sound," said pollster Madonna.

Against that backdrop, Madonna said that Toomey has been "a strong and consistent supporter" of the gas industry, while McGinty has favored addressing environmental concerns with regulation.

"I never got the sense she led a crusade on this," said Madonna. "She's not a crusader."

In the Democratic primary, she said her opponents who were calling for an outright fracking ban were peddling sound bites instead of policy. McGinty maintained the endorsements from LCV and other environmentalists demonstrates their faith in her resolve to work for cleaner energy. "The bottom line is I'm supported by solar and wind energy," she said. "I'm not supported by the frackers and drillers."

In the head-to-head fight between McGinty and Toomey, fracking has faded as a central issue. If energy is discussed at all, it's as a subset of the overarching issues of economic opportunities and costs for ordinary Pennsylvanians. When McGinty brings up climate change, she talks about how clean energy would help the middle class: "We should seize the opportunity to create good jobs and cut electricity bills," she said in a statement on the Paris treaty talks.

Toomey and his allies, meanwhile, have sought to hammer home the message that support for renewable energy has been a costly boondoggle. They attack McGinty for taking jobs on the boards of a renewable energy company and a utility that did business in the state, Iberdola and NRG Energy, after leaving the Rendell administration. "She helped them get our money, they helped her career," says one ad by the Koch-funded Freedom Partners Action Fund. Freedom Partners points out that one wind energy company McGinty brought to the state ended up closing its doors (though it doesn't mention that was due to Congress allowing federal tax subsidies to lapse).

Clinton's Potentially Long Tail

But the outcome of the Pennsylvania Senate race, longtime political observers agree, is deeply dependent on the presidential race. Over time, the state's voters have become less likely to split tickets in the ballot box, Madonna said. When President Obama won Pennsylvania by 5.2 points in 2012, it gave Democrats enough of a boost that they won every statewide race for the first time since the 1970s. Alan Novak, former chair of the state Republican Party, said last week in an interview with The Philadelphia Inquirer that Toomey would have difficulty if Clinton pulled ahead of Donald Trump by more than 5 points in the state. Clinton was ahead by an average of 8.6 points in Pennsylvania last week, according to RealClearPolitics.

McGinty has focused on tying Toomey to Trump. Toomey has not endorsed Trump, but McGinty has goaded Toomey for not going far enough to denounce the GOP standard-bearer.

McGinty has also gotten help from Clinton's star surrogates, Bernie Sanders and Elizabeth Warren, who've visited Pennsylvania to campaign with her.

Toomey's early advantage in the polls, by as much as 10 points in July, has evaporated as Clinton's lead over Trump in Pennsylvania has solidified. Recent polls have Toomey and McGinty in a dead tie, according to RealClearPolitics.

On election night, interest in this race will extend far beyond Pennsylvania, with the direction of climate policy in the next Senate hanging in the balance.