The fate of the two bills is sure to echo beyond the Pacific Northwest, as activists, governors, and state legislators around the country will take their examples as either inspiration or warning. The bills will also define national climate policy to come: Just as Massachusetts’s health-care reform in 2006 shaped the Affordable Care Act, state efforts to rein in climate change today will inform future national Democratic legislation.

The Washington statehouse has failed to affirm climate policies at least twice before. Inslee says he hasn’t given up yet, and The New York Times has reported that he may try to put a carbon tax on the state ballot in November. But the bill that failed Thursday differed from any other state-level climate policy pursued in the United States.

“It’s a carbon tax. That’s unique,” said Kristin Eberhard, a senior researcher at the Sightline Institute, a left-leaning think tank based in the Pacific Northwest. “Carbon taxes have not made it very far through any state legislature. There’s no state-level carbon tax in the United States.”

Most economists consider a carbon tax the most efficient way to address climate change. Instead of forcing every industry to follow a different set of climate-focused regulations, a carbon tax evenly accounts for the costs of climate change across the economy, they argue. Over time, the higher prices of fossil fuels will spur companies and consumers to opt for cleaner technology.

The proposed carbon tax in Washington would have imposed a $12 tax on every ton of carbon pollution. This is pretty cheap, as carbon taxes go: The Obama administration once estimated a U.S. carbon tax should run at about $40 per ton.

“It would not be very stringent globally,” Eberhard told me. “But it would be groundbreaking just in being a state-level carbon tax in the United States.”

The tax would cover the vast majority of greenhouse-gas emissions from Washington. Gas prices would rise at the pump, as would the cost of home-heating oil and natural gas. Factories would have to track and pay for their carbon-dioxide emissions, and consumers and companies would also see their electricity bills go up. Any power generated with fossil fuels out of state—by a coal-fired power plant in Idaho, for instance—would be affected by the tax.

The tax would not charge residents for the costs of so-called embedded carbon emissions in consumer or commercial goods, such as the crude-oil-derived products in paints and household cleaners.

The millions of dollars in new revenue from the carbon tax would have been invested in clean-energy projects, water and natural-resource preservation, and assistance for workers who were employed in the fossil-fuel industry.

Some climate policies—such as the Republican-friendly “Baker-Shultz” plan—have proposed sending any new revenue back to taxpayers in the form of a monthly check. But some climate hawks on the left believe this policy will have little effect on emissions. In 2016, Washington voters rejected a revenue-neutral carbon tax in a ballot referendum opposed by both the center-right and the left.