The move to defeat Proposition CC appears to have succeeded Tuesday night, as Coloradans weighed in on giving up part of their future tax returns to fund education and transportation.
The measure fell behind early and struggled to keep up until the opposition declared victory within the hour after polls closed.
Opponents of the measure lead with 55% of votes as of 9:27 p.m. Tuesday, with 30 of 64 counties reporting.
"I think voters understood clearly this is a significant tax increase," said the state's last Republican governor, Bill Owens. "This is simply a way for government to get more money without making the case for it."
State Speaker of the House KC Becker, who authored Proposition CC, declared its failure Tuesday night, but said "we must keep moving forward."
Proponents for the ballot question campaigned on raising hundreds of millions of dollars without raising taxes, but Jesse Mallory, the director of Americans for Prosperity in Colorado, the main driver of the opposition effort, said voters saw through that.
"If you're paying more in taxes than you otherwise would, the average person would call that a tax increase," he said.
Proposition CC asked Coloradans to forever forego their occasional tax rebates under the state constitution's Taxpayer's Bill of Rights to instead plow hundreds of millions of dollars into education and transportation. The windfall would be split between K-12 schools, higher education and transportation.
The GOP took a voter turnout advantage into the final days, with better than 36% of the returned ballots from registered Republicans. Democrats turned in about 31% as of Tuesday afternoon, according to the Secretary of State's Office. Unaffiliated voters made up the rest. A University of Colorado online survey released Monday indicated that Proposition CC was trailing by 7%.
Michael Fields, the executive director of the conservative advocacy group Colorado Rising Action, who led debates against the ballot measure, called it a team win.
"We were up against misleading ballot language and millions of dollars of out-of-state money pouring in against us, but thankfully our Taxpayer’s Bill of Rights is preserved," he said in a statement. "Voters clearly pushed back against the overreach coming from the legislature and governor last session."
U.S. Rep, Ken Buck, who chairs the Colorado Republican Party, called taxpayers the winners.
"Governor Polis and the liberal state legislature overreached once again but were unsuccessful in deceiving the voters of Colorado to fund their reckless spending spree," he stated.
At the Yes on CC watch party in Denver, Amie Baca-Oehlert, the president of the Colorado Education Association, said proponents remained "super hopeful."
"Obviously, school funding in Colorado, plus our roads and higher-ed have been a problem for years," she said. "We would love for Prop CC to pass tonight as a stepping stone to continue to build off of the work on funding, because it is not the ultimate solution."
She noted that voters frequently forego their TABOR refunds on the local level, and she was hoping they would step up at the state level Tuesday night.
"If the voters were to do this tonight at the state level, I think it sends a really strong message on our values, and where we stand with the public services that we want in Colorado," she said.
The refunds are triggered when tax revenue exceeds that the spending cap, calculated on inflation and population growth. Coloradans have received rebates in only nine of the 26 years since TABOR became law.
Because the beneficiaries of Proposition CC couldn't count on the money every year, or potentially any years, its use was tabbed to one-time projects, teacher bonuses or curbs on tuition increases.
TABOR refunds flow first to property tax exemptions for disabled veterans and the elderly, then whatever's left is passed on through temporary reductions in sales and income taxes.
Conservatives see TABOR, the only measure of its kind in the nation, and its spending cap as their best tool to prevent Democrats from spending wildly on social programs.
Progressives see TABOR as a shackle on the state budget investing in schools, roads and other demands of population and commercial growth.
Voters in cities, counties, school districts and other subdivisions of government have routinely opted out their jurisdiction from the constitutional spending cap to pay for local projects. Save a five-year TABOR timeout passed in 2005 to shore up a shaky state budget, Colorado voters have stood steadfastly behind the measure.
The opposition to Tuesday's ballot measure was led by some of the state's best-known Republicans, including state GOP chairman Ken Buck, University of Colorado regent at-large Heidi Ganahl and 18th Judicial District Attorney George Brauchler, the party nominee for attorney general last year.
Despite the loss, Lisa Weil, executive director of the advocacy organization Great Education Colorado, called Proposition CC a step in the right direction.
“I think there is an understanding that we are not able to address the growth that’s happened in the last few years to maintain the quality of life,” she said.
“Proposition CC is just a really common-sense way to say at least can we keep the revenues that are coming in because of the vitality of our economy and use those to invest in the things that we care about.”
Ganahl, the co-chair of the No on CC campaign, made an 11th-hour pitch on social media Monday night.
"My Colorado friends, you are waking up tomorrow morning to a choice," the likely candidate for higher office in the near future wrote on her Facebook page. "Our state population has grown 15% in a decade, our state budget has grown 71%. Don't let them take your refund away forever (and yes, it's a tax increase). They have a spending problem, not a revenue problem."
Proposition CC was voted onto the ballot in the spring by the General Assembly, picking up just one Republican vote in the 100-member legislature, Sen. Kevin Priola of Henderson, who co-sponsored the bill.
Voters statewide passed TABOR in 1992, the first election that Priola was old enough to vote in, he said. He supported then and he still supports it now.
"This is a great opportunity to invest without any new taxes," Priola said last month.
Supporters of the ballot measure portrayed it as a way to raise money without raising taxes, but the opposition made a case that taking away a tax refund, by any other name, is still the government keeping money that would otherwise belong to taxpayers.
Though it has since been rebranded as a vehicle to limit growth in government it was sold mainly to voters as a way to assure them a direct vote on tax hikes and other major government spending decisions.
Proposition CC would not affect voters' ability to weigh in on future taxing and spending.
Colorado Politics' Alayna Alvarez contributed to this report.