Democrat Mike Levin has made his bid to win a House seat long occupied by Republican Rep. Darrell Issa all about climate change — and it looks like it’s working.

Levin kicked off his campaign nearly two years ago — before Issa, a leading antagonist of President Barack Obama’s administration, announced his retirement — by sending the nine-term congressman a book titled Climate Change for Beginners. In the final stretch, Levin’s continued to make his background as a former environmental lawyer and the threats of climate change a central issue of the campaign.

Though the Democratic Party has long pushed for action to combat global warming, it’s unusual to see a candidate put the issue front and center. Last cycle, the Democrat who came within one percentage point of Issa talked about climate change as one of the leading threats to the U.S., but it was low down on the list of issues raised when first engaging a voter. Often, Democrats will have a line on their campaign websites, committing to support renewable energy and proposals to limit carbon emissions, but typically don’t bring it up much until asked at campaign events.

Levin has run his race differently. At a recent meet-and-greet in an affluent Encinitas enclave, climate change was the first policy issue Levin mentioned in his stump speech.

“Who here saw the IPCC report on climate change?” Levin asked the crowd, referring to the October report from the United Nations Intergovernmental Panel on Climate Change.

“What it said in a nutshell — I’ll save you some time — we’ve got about 15 years to take action,” said Levin. “We’ve got to have a Congress that leads again on climate change, leads again on sustainability, and while we do it, we’re going to create the great jobs of the future in clean energy.”

Levin’s targeted his opponent, Republican Diane Harkey, on the issue, frequently citing an answer of Harkey’s in an interview with the San Diego Tribune.

“I am not a scientist,” Harkey told the local paper. “I can’t read all of that stuff and make a decision. It’s not where I was educated. I’m an economist person.”

Harkey, like President Trump, points the finger at China and India when discussing climate change, arguing that the U.S. is shouldering too much of the burden. Trump pulled the U.S. out of the Paris climate pact.

“I don’t think we have the luxury of being so uninformed in a district that has some of the leading scientists in the world,” Levin said to a friendly crowd in Encinitas. The district includes part of the Scripps Institute of Oceanography, a research department of University of California, San Diego.

Harkey “believes that climate change is a serious issue that requires government and private industry to work together to address” said Dave Gillard, Harkey’s consultant. He added that Levin’s alignment with Sen. Bernie Sanders, I-Vt., makes him “too liberal for the district.”

Gillard took aim at GOP PACs for not investing in the race in the final stretch as some have written off the race given Levin’s lead.

“It is too bad the major Republican PACs choose not to spend in the 49th [Congressional District],” said Gillard.

Hillary Clinton won the district by 8 points, making it a top target for Democrats this cycle. And the demographics of the once-reliably red district have swung dramatically toward Democrats in the last decade. The new makeup of the district likely factored into Issa’s decision to retire at the end of his term. He won re-election in 2016 by less than one percentage point.

There are more Democrats than Republicans in the large portion of the district that’s located inside San Diego County.

A New York Times poll from last week found Levin leading Harkey by 14 points. And FiveThirtyEight projects Levin has a 97 percent chance of flipping the seat. Harkey has pushed back, citing internal polling that put her in a “dead heat” with Levin.

A sign of the changing dynamics in the district, Levin doesn’t shy away from riling up voters with talk of what a Democratic-controlled House would do.

“If we had a Democratic House we are going to see the president’s tax returns,” Levin said to cheers in Encinitas. “It’s not about the I-word, it’s about the rule of law.”

Levin’s success is in large part due to Issa, who held the seat for 18 years as the district shifted under him. As animosity for Issa grew among his constituents, more residents mobilized and began holding rallies outside his office. Remnants of the campaign Levin never got to run are still scattered throughout his San Clemente field office — a “dISSApointment” sign taped to the wall. Issa may not be on the ballot anymore, but Levin’s campaign is organizing one final protest outside Issa’s district office on Election Day.

Much of Levin’s support on the ground and over the airwaves has come from leading environmental groups. The League of Conservation Voters is spending more than $800,000 in San Diego County. Former New York Mayor Mike Bloomberg, who is flirting with a 2020 run, is spending roughly $1.4 million in support of Levin on ads in the more expensive Los Angeles media market, which blankets the south Orange County section of the district.