Jared Polis, a Democrat for Lower Taxes

It’s part of a growing nationwide movement for state tax relief. Legislatures in 10 states reduced income taxes this year; 11 did in 2021. In 2018 Kentucky became the fourth state in history to move from a progressive personal income tax to a flat rate. This year four more states began such a transition.

Colorado’s Proposition 121 would reduce the state’s flat rate for both individuals and corporations to 4.4%. Voters approved a rate cut from 4.63% to 4.55% with Proposition 116 in 2020.

Rather than resist this movement, as other Democratic governors have, Mr. Polis has ridden the wave. He supported both ballot measures. That has kept him and his party popular even though Colorado has had the highest inflation of any state since the start of last year, according to the State Inflation Tracker, a project of Republicans on the congressional Joint Budget Committee.

“We celebrate every step of progress along the way,” Mr. Polis said after proposing elimination of Colorado’s income tax and praising Proposition 116 last summer. “It’s not zero or nothing.”

The Independence Institute, my think tank, calls our incremental approach the “path to zero.” The institute’s plan answers Mr. Polis’s call to phase out the income tax without jeopardizing the state budget. To accomplish this, it uses a ratchet-down mechanism that would lower the income tax rate during years in which the state experiences a revenue surplus, ultimately taking the rate to zero.

While states across the nation have seen a move toward lower taxes, Colorado stands out as a blue state that is making meaningful progress. Mr. Polis is the only Democratic governor who supports abolishing the income tax.

Democrats in other states should pay attention. With inflation at 40-year highs after a bout of unprecedented government spending, the push to limit growth of government and let people keep more of what they earn is a direct response to the economic woes Americans now face.

By getting on the right side of the tax-relief movement, Mr. Polis may help Democrats in Colorado buck the nationwide move against the Democrats and stay in power even if this week’s elections produce a red wave. He made the political calculation in his bid for re-election to endorse Proposition 121’s tax cut and advocate for the elimination of the income tax. To keep that appeal relevant if voters re-elect him, he will need to follow through on his rhetoric by putting Colorado on a path to zero income tax during his second term.

Mr. Murrey is director of the Independence Institute’s Fiscal Policy Center.