Those who know incumbent Republican Mike Coffman of Aurora say he’s the hardest working man in politics. Given this election year and demographic and political makeup of his suburban district, he better be.

Coffman is fighting for re-election in one of the most competitive congressional elections in the country.

“This is the race of Coffman’s career,” says David Wasserman, who handicaps U.S. House races for the Cook Political Report and labels the 6th District as a tossup.

A once solidly Republican district, the 6th has morphed into one more favorable to Democrats after the latest round of gerrymandering. The 2012 redrawing of district boundaries folded in sizable Latino and Ethiopian populations.

Even so, Coffman has proven tough to beat. Taking him on this time is Morgan Carroll, a liberal state senator from the area whom Democrats insist is a better candidate than those who came before her, especially in a presidential election year analysts say is likely to turn out more Democrats and left-leaning voters than in 2014.

Meanwhile, Donald Trump at the top of the ticket has caused headaches for Coffman, a retired Marine who became the first Republican congressman to air a TV ad critical of Trump. “Honestly, I don’t care for him much,” Coffman says in the ad, promising to “stand up” to Trump if he becomes president.

Both candidates have raised more than $1 million each in the lead-up to the Nov. 8 election and the race has become a priority for the conservative Americans for Prosperity. In fact, the race is the only congressional election in the country in which the group, backed by the billionaire industrialist Koch brothers, is actively campaigning for the defeat of a candidate rather than focusing on voter education. Carroll’s record on taxes and health care are untenable, the group says.

“This is only the second time in 10 years in Colorado that we have decided to advocate for someone’s defeat,” AFP state director Michael Fields told The Colorado Independent. The first was Democrat Mark Udall in the 2014 U.S. Senate race, which Udall lost.

AFP’s volunteers have knocked on more than 50,000 doors in the district. The group also has made phone calls and is doing direct mail.

In another sign of just how important the race is nationally, Republican Speaker of the House Paul Ryan was recently in town to support Coffman, while former Democratic Speaker of the House Nancy Pelosi swung through for a pro-Carroll event.

So, why is this race so important this year?

Frankly, a race between a credible challenger and Mike Coffman likely would get attention in any year. Once a conservative stronghold that sent controversial Congressman Tom Tancredo to Capitol Hill, the district was redrawn after the 2010 census as one more friendly to Democrats.

Anchored by Aurora and encompassing the Denver suburbs south to Highlands Ranch and east a few miles beyond DIA, it is now a swing district in a swing state. That it gives Democrats an opportunity to pick up a seat in the Republican-controlled House is enough to warrant its value to both parties.

One in five district residents is Latino and 15 percent are foreign-born. How this race turns out might offer both parties a blueprint for how to connect to one of the fastest-growing voting blocs in the country.

Voters there are also now almost evenly divided among Democrats, Republicans, and those who are unaffiliated.

In the old 6th, Coffman pushed a bill to make English the nation’s official language and “suggested that Hispanic voters who could not understand their ballots should ‘pull out a dictionary.’” In the new 6th, he has taught himself Spanish.

Coffman’s political messaging has been designed to portray him as a friend of immigrants. As one TV ad puts it, “He’s not like other Republicans.”

Coffman’s 180 in response to his district’s changing demographics has led University of Denver political scientist Seth Masket to ask if what the Congressman is doing is “shameless pandering” or “good representation.”

In 2012, the first race in the new 6th, Coffman defeated then-Democratic Rep. Joe Miklosi by only two points. Two years later. he faced former Democratic Speaker of the House Andrew Romanoff in a race that at the time was framed as one of the few competitive U.S. House races in the country. Coffman clobbered Romanoff. In that off-year election, Democrats also didn’t turn out as much as Republicans.

Though Coffman has been victorious in a more Democratic district than the one to which he was first elected in 2008, the Cook Political Report’s Wasserman says this may be the race of his career. “This is the first time he’s had a combination of a presidential year and a formidable opponent in that district,” he said.

And there’s big money in this race, of course?

Yep. As mentioned, Coffman and Carroll have each raised more than $1 million apiece and spent about the same. And already more than $10 million has been set aside for the race, according to public money-in-politics filings.

The political arms of the national Democratic and Republican parties have set aside around $6 million and $5 million in airtime for the election, respectively, reports Sandra Fish who broke down the ad spending on Aug. 15 for Colorado Public Radio.

Other groups are air dropping support into the suburban district, as well, with tens of thousands here, and hundreds of thousands there. Coffman’s top five campaign contributors this cycle have been land title companies, lawyers, Bloomin’ Brands, which owns the Outback Steakhouse restaurant chains, an auditing firm, and the Texas Republicans United PAC, according to the Center for Responsive Politics.

A Super PAC called Immigrant Voters Win is supporting Carroll in the race, and has spent more than $10,000 so far. She is also backed by Planned Parenthood Action Fund, and the pro-choice groups Emily’s List and NARAL Pro-Choice Colorado.

Is the U.S. House even up for grabs this year?

Early on in this election cycle, most prognosticators likely would have said no. Republicans currently hold the largest majority they have had in the U.S. House since 1928, controlling 247 seats compared to the 188 held by the Dems.

In Colorado there are four Republican members of Congress and three Democrats.

Plus, in modern times, U.S. House districts have been gerrymandered in order to provide safe seats for incumbents, candidates, or particular political parties, all across the country.

That, mixed with geography and what political scientists call “self-sorting”— or people moving into areas where like-minded neighbors live— means competitive districts are rare.

But this year, with Trump on top of the ticket, Democrats are also expanding their map and looking at races they might normally write off. (Not that they would have written off the 6th.) So, one theory goes that Trump is such an electoral disaster — “a trainwreck of a candidate” is how Carroll describes him — that he will turn voters away from Republicans down the ballot in congressional races across the country, giving Democrats a chance of picking up 30 seats to gain a majority.

OK, so who are Mike Coffman and Morgan Carroll?

Mike Coffman: Republican shapeshifter

Coffman is a military guy who quit high school to join the Army, earn his diploma while in service, become a Marine, start a property management company, and work his way up the political ladder from state representative to state senator to state treasurer to secretary of state, and, eventually, to congressman.

He is, as he notes on his congressional website, “the only veteran in the Colorado delegation and the only member of Congress to have served in both Iraq Wars.” He was an infantry officer in the first Gulf War, and in 2005 served as a civil affairs officer supporting the Independent Electoral Commission of Iraq. The Washington Post fact-checked Coffman’s bio claim that he was a “combat veteran,” and came away convinced.

Throughout his time in Congress, Coffman founded the first Balanced Budget Amendment caucus, and his campaign touts his score from the Lugar Center as the 25th most bipartisan member of Congress in 2015.

Coffman, 61, with a trim build and thinning gray hair, is known as a workhorse on the campaign trail, a master of the rubber-chicken event circuit.

“I think he’s one of the hardest working men in politics,” says his friend Jon Caldara who heads the Denver-based libertarian Independence Institute think tank and would see the candidate at every political event in the area.

“He wouldn’t leave until he shook the hand of every man, woman and child in the place,” Caldara says. “When it comes to connecting with voters, man, he’s there.”

In one of his first TV ads of the election, titled “One of Us,” supporters from different ethnic backgrounds say “Nobody works harder than Mike.” The ad is likely meant to soften up a candidate known as a hardliner on immigration reform and a vocal supporter of anti-immigrant former Congressman and gubernatorial candidate Tom Tancredo, who previously held Coffman’s seat in Congress.

In Colorado, Coffman, who is married to GOP Attorney General Cynthia Coffman, has been a slippery target for the left. He has adapted to his changing district — and, perhaps, the times — in a way that has insulated him from the kinds of gaffe-prone defeats of his congressional colleagues.

In 2012, for instance, Coffman said of President Barack Obama, “I don’t know whether Barack Obama was born in the United States of America. I don’t know that … But I do know this, that in his heart, he’s not an American. He’s just not an American.”

Coffman later apologized and said he misspoke. The gaffe wasn’t enough to cost him reelection in 2014 when Obama carried the district. Coffman is now running under the banner of a presidential nominee who essentially brought the birther movement into the mainstream.

Coffman also has called himself a “proud member” of “the party of ‘no’” during a speech he gave under waving Don’t Tread on Me flags in the heat of the Tea Party fever. And last year he spoke at an event for ACT for America, described by the hate-group tracking Southern Poverty Law Center as “perhaps the nation’s leading anti-Muslim hate group.” A Coffman spokeswoman later explained the Congressman speaks to hundreds of groups and very rarely agrees with every aspect of their agenda.

Carroll’s campaign has used all these missteps and past positions to accuse Coffman of laying the groundwork for the kind of hateful messaging around immigrants and others that has been spread by Trump. She has tried to tie Coffman to Trump to the point that Coffman told one reporter: “She has to make her campaign about Donald Trump. … If it’s about me, she loses.”

Related: Morgan Carroll calls Mike Coffman Trump-like, but is it true?

These days, voters can find Coffman learning Spanish at night and spending his days at events such as a local Ethiopian festival, earning headlines in The New York Times that read “A Congressman Slighted Immigrants, Then Embraced Them. Now He Runs From Trump.”

Recently, the political DC publication Roll Call wrote how Coffman wasn’t on its list of the 10 most vulnerable incumbents because “he’s a four-term incumbent who’s said he’ll try to distance himself from Trump.”

Coffman’s campaign is stressing his work on issues that are nowhere near the kind of red-meat conservative policy positions of the Tea Party movement of 2010.

For instance, his campaign says Coffman is most proud of sponsoring bills that would permit the Veterans Administratio to do mental health screening and counseling for vets with other-than-honorable discharges, allow first-time homeowners to withdraw $15,000 more from their IRA’s for a down payment, and increase the Earned Income Tax Credit, among others. He was also the first GOP sponsor of The Pregnant Workers Fairness Act, which would make employers accommodate pregnant workers rather than forcing them out of their jobs.

And the campaign points to work he has done on LGBT issues such as supporting the Employment Nondiscrimination Act (ENDA), which earned him kudos from groups like One Colorado. The campaign also points to how his support of the LGBT-inclusive Violence Against Women Act earned him praise from Planned Parenthood. Two years later, Coffman voted on a budget bill that would defund the group because it provides abortions.

As he campaigns this year, Coffman’s staff also portrays him as a congressman who has stood up to his party’s leadership and worked behind the scenes on immigration reform.

In 2012, Obama beat Mitt Romney by 5 percent in the newly redrawn district, and yet Coffman out-performed Romney, the Republican nominee for president, by a few points, showing he pulled support from non-Republican voters.

Coffman declined repeated requests for an interview for this piece. His campaign says that if reelected, he would fight to reign in spending, balance the budget, and defend whistleblowers.

On immigration, a key issue in the district, Coffman “will continue to fight for a step-by-step approach that protects our borders, creates certainty and permanence for law-abiding undocumenteds, keeps families together, and brings a real resolution to a debate that has been ugly and divisive,” said his campaign spokeswoman Cinnamon Watson.

Asked if she could be more specific about whether he currently backs a bill or is working on one and could outline certain policies in it, she did not immediately respond.

Carroll: Progressive firebrand

In 2013, when Democrats controlled the Senate in Colorado, Morgan Carroll was their leader. She has represented voters in the district for the past 12 years. Direct and to-the-point in person, and a self-styled policy wonk, she claims to have read the entire Obamacare bill twice and told The New York Times she read every bill on which she has ever voted in Colorado.

Carroll, 44, is a liberal who doesn’t hesitate to use strong language to describe the opposition party. During a speech to caucus-goers outside Denver in March, she called Republicans “nut jobs” and fascists.

Carroll is running on her record of passing progressive bipartisan legislation in a divided state statehouse. She says when she was Senate president she made a point to meet every senator to see if there was legislation on which they could find common ground. She tells voters that is what’s lacking in Washington. Her campaign slogan is “Let’s get real results.”

Just after Labor Day, Carroll released her first TV ad, in which she says “Congress is broken” and promises to fight to make college affordable and to create good-paying jobs.

“I worked in gas stations, I worked in pizza delivery, I worked in fast food, and tried very hard to save money so that I might be able to go to college,” she says in the ad. “I know what it was like to work for minimum wage.”

Late last month, Carroll sat on a panel about higher education and talked about how her mother was the first in her family to go to college. She had no money, but she got into the University of Denver and received a full-ride scholarship for law school, Carroll said of her mother. Higher ed degrees are “realistically a non-option” for many people now because of the way education is financed and a student loan crisis, Carroll said.

As a congresswoman, she told the crowd recently at a downtown Denver pub, she would work on a law that would lower interest rates on student loans and allow for refinancing under more favorable terms. She would also look at forgiving student loan debt altogether if a graduate goes to work in a certain job or area.

“We can’t get a Congress right now that’s willing to take up a bill or debate the issue,” she said, calling that “legislative malfeasance” and “obnoxious.”

But why would someone who talks so much about what she has been able to do for Colorado want to enter a gridlocked Congress where nothing gets done? Her answer: She couldn’t stand by and do nothing. Carroll says she is convinced if she gets to Congress she’ll be able to get things done by finding common ground with opponents as she did as Senate majority leader in Colorado.

“All those things that got done in terms of tangible results? I didn’t do any of that by myself,” she told The Independent. “Everything takes other people to do it. But the power of one person is to have the vision and the leadership to do the work that is necessary in order to bring the issue up to the forefront, in order to be a driver to insist it has to happen.”

She frames the race around a vote for someone with a proven record of results versus a sitting member of a do-nothing Congress.

“I have a record I’m proud of,” Carroll says about helping pass more than 100 state reforms. “Not little, fluffy stuff, not cosmetic stuff,” she adds, noting that she passed lobbying reform, campaign finance reform, helped double the state’s renewable energy standards, and quadruple rooftop solar. She says she helped bring three new companies to the state and brought in $60 million in cost savings with mental health treatment as part of criminal justice reform.

Some of those reforms were controversial, such as the 2013 gun laws Democrats passed that created universal background checks and limited the number of bullets a gun magazine could hold to 15. That package of laws resulted in three Democrats losing their seats in unprecedented recall elections.

She also drew fire from some Latinos in 2009 when she joined Republicans and a handful of Democrats to help kill a bill that would have allowed in-state tuition to the children of undocumented immigrants. (She said she worried the bill was in conflict with federal law and could get Colorado sued. Carroll later supported the measure, which passed in 2013.)

Carroll paints Coffman as a political chameleon — “a little like Jell-O”— whose skilled marketing has paid off in previous elections in which more Republicans turned out than Democrats.

“No one questions that Mike Coffman is a hard-working campaigner,” she says. “The bigger problem is what has he done for the people of this district — not said— but what has he [done], and does his walk match his talk? It doesn’t. The one thing that has been consistent is he will do and say anything to get elected.”

And she blames Coffman for the rise of Trump’s rhetoric.

“When Mike Coffman tells people to go get a dictionary when it comes to vote, or when he’s keynoting for an anti-Islamic hate group, that’s not Trump, that’s Mike Coffman,” she says. “And Mike Coffman was doing that before Donald Trump even had a twinkle in his eye about running for president.”

But just as Carroll links Coffman to Trump, Coffman has linked Carroll to Hillary Clinton.

“Hillary defended the VA. State Sen. Carroll said nothing,” Coffman wrote on his Facebook page, about Clinton saying she thought problems at the Veterans Administration were being overblown. “Hillary supports the Iran Deal and Obamacare, she trashed charter schools and called for the closure of Guantanamo Bay. And all we get from state Sen. Carroll is silence or ‘me too.’ Hillary and the Democrats even rigged the election to the disadvantage of Bernie Sanders. More silence. More complicity.”

Carroll gave a low-key endorsement of Clinton in early July, but she disagrees with Clinton about the war in Iraq and the PATRIOT Act, and she opposes the Trans-Pacific Partnership, a global trade agreement about which Clinton has waffled.

Related: Opponents seek to define Morgan Carroll in the mold of Hillary Clinton

“To me it’s a question of do something versus do nothing,” Carroll says about why voters in the 6th District should choose her. “It’s a question of substance versus appearance. And it’s a dispositional question of whether you’re willing to walk the walk and take up the fights that need to be done, and sometimes it’s not always popular.”

Coffman is distancing himself from Trump. What does that mean?

In August, the Republican incumbent did something no other sitting Republican member of Congress who is up for re-election did. He took on Donald Trump directly in a TV ad.

Why? The district, packed with immigrants and suburban women, is not likely fertile ground for Trump’s angry strongman schtick. It is not, say, rural Alabama. So Coffman had to make a choice: Stick with the presidential nominee of his party or run against him.

“We have this race in [our] toss up [category] and the only route for reelection for Coffman is to distance himself from Trump,” says Wasserman of the Cook Political Report. “He has no choice. This is not going to be a good district for Donald Trump. [Coffman] is making a smart move by jabbing not only Trump but also Clinton in his commercials.”

But doing so has created some heat on Coffman’s right flank from loud Trumpists like former Congressman Tom Tancredo, who has already been breathing fire at the man who once called Tancredo “my hero.”

Speaking on an Aug. 11 conservative talk radio show, Tancredo said conservatives would “lose nothing” if Coffman were defeated. Tancredo said on KNUS he believed if Trump were polling well in the district, Coffman would support him. “As his district changes, so does he,” Tancredo said. “He sort of morphs into a different person.”

A big question for this election will be whether Coffman can win over enough unaffiliated voters in the district who don’t like Trump to make up for the hardcore conservatives who might peel off from him for his anti-Trump stance.

Carroll has come out against the ColoradoCare universal healthcare ballot measure. What does that mean?

Last month, ProgressNow Colorado held a news conference in which it denounced Amendment 69, aka ColoradoCare, the ballot measure to provide universal healthcare in Colorado. A few days later, Carroll did the same.

“I believe that the American people today are paying too much money for too little health care — but I am not supporting Amendment 69,” she said in a statement. “The rising cost of drugs is one of the biggest contributors to soaring health care costs and really must be solved at the national level with policies like negotiating drug prices for Medicare.”

Carroll had earlier supported having a universal healthcare system in Colorado.

Her opposition to Amendment 69 is likely to help Carroll with establishment Democrats and business interests in the district at the expense of some in the Bernie-or-bust progressive base who support healthcare for all and are championing ColoradoCare.

A question for Carroll will be whether her anti-ColoradoCare stance will draw enough moderate voters to make up for supporters of Bernie Sanders and the health care measure who might cast their ballots for a third-party option as a protest vote.

Is there a third-party option on the ballot this year?

Yes. Robert Lee Worthey, a leather jacket-clad music educator who moved to Colorado last year from Alabama, will be on the ballot as the Green Party’s nominee in the 6th District.

Worthey supports ColoradoCare.

A large part of his platform is renters’ rights, student loans and climate change.

When introducing Worthey to a Green Party group in April, Sean Friend, co-chair of the Arapahoe County Green Party, said Worthey was running “to give us, obviously, name recognition, get somebody on the ballot, somebody to challenge Coffman, who is currently in office, who needs to go.”

When will Coffman and Carroll debate?

So far three debates are scheduled.

Entravision will air on one Oct. 8, CBS4-KBDI will air on Oct. 14, and 9News in Denver will air a debate on Oct. 20.