Polis' Republican opponent, state Treasurer Walker Stapleton, is appealing to Colorado's large independent voting bloc, calling the liberal Polis "too extreme" for Colorado. He argues Colorado cannot afford Polis' ideas for tackling underfunded schools and roads and renewable energy standards.
"You have no way to pay for any of this," Stapleton told Polis in a recent Denver debate. "You're the most radical, extreme person in Colorado's history."
"Dream. Dare. Do," Polis urged in a Saturday night forum in Pueblo. "We gotta think big, folks."
Republicans are seeking to capture a Colorado governor's seat they haven't held since 2007 to go with their control of the state Senate, a 4-3 edge in its congressional delegation and the statewide offices of treasurer, attorney general and secretary of state posts. Democrats are banking on an anti-Trump "blue wave" to flip the Senate and consolidate control of the statehouse.
Under Hickenlooper, Colorado has one of the nation's lowest unemployment rates and highest rates of economic growth, largely fueled by the tech, aerospace and oil and gas industries. Stapleton insists Colorado owes its prosperity to conservative fiscal policy.
Polis, a tech and education entrepreneur, aims to become Colorado's first openly gay governor. The five-term congressman has poured roughly $20 million into his campaign.
Stapleton had raised $3.2 million as of Oct. 1. He's campaigned on his record as a steward of the state's accounts, his efforts to rescue an underfunded state pension system and his defense of requiring voter approval of statewide tax hikes and bond issues.
The two have clashed over Polis' proposals for single-payer health care. Polis insists a statewide or regional health care exchange will shore up a system that, under the Affordable Care Act, has left many rural Coloradans with a single insurer and some of the highest health insurance premiums in the country.
Stapleton supported the Trump administration's efforts to dismantle the act. He's recently insisted that he'll defend the expansion of Medicaid, which covers nearly one in four Coloradans.
With this spring's teacher protests over pay and resources still resonating, Polis - a onetime state education commissioner who has founded several schools for the underserved - says Colorado should adopt a version of Oklahoma's universal preschool program. He's also suggested going to the voters to boost K-12 funding.
Stapleton says Colorado's K-12 schools - dozens of which have been forced to adopt four-day weeks - have enough money to be fully funded by cutting what he calls bloated administrative overhead.
The candidates diverge starkly on energy policy. Polis is proposing to power Colorado's energy grid from all renewable sources by 2040, a plan that Stapleton says would put more than 300,000 jobs at risk. Polis counters that Colorado would remain an exporter of oil and gas and that climate change demands action.
The two also disagree about guns - a perennial issue in a state rocked by the 1999 Columbine High School and 2012 Aurora movie theater shootings.
Polis calls for a "red flag" law that would suspend access to firearms for persons deemed by a court to be a threat to themselves or others. Senate Republicans defeated similar legislation this year despite the New Year's Eve shooting death of a suburban Denver sheriff's deputy by a man known to have threatened violence.
Stapleton, backed by gun rights groups, not only opposes such a law but also existing Colorado bans on high-capacity magazines and added background checks passed after the Aurora killings.
National politics will enter the race in its final weeks, with Trump formally endorsing Stapleton on Wednesday and independent Vermont Sen. Bernie Sanders planning appearances for Polis later this month.
"We think stumping with Bernie will backfire for Polis, because it will remind voters of how far left he'd like to take Colorado," said Jeff Hays, the state's Republican chairman.
"It's no wonder Donald Trump is supporting Walker Stapleton so enthusiastically," countered Polis, "because he couldn't have asked for a better yes-man for his destructive policies."
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