Most Coloradans know that the Taxpayers Bill of Rights, or TABOR, limits the growth of the state budget. When the state takes in more revenue than what the TABOR formula allows, it's supposed to refund the excess.

That's only happened once in the last 14 years. Even so, Democrats in the statehouse approved a November ballot issue — Proposition CC — asking voters to permanently eliminate the TABOR cap and allow any extra money to be spent on education and transportation.

The Legislature authorized the question before state economists projected the state would collect about $1.3 billion over the TABOR cap during the next three years. Prop CC doesn't include the projected $575 million excess from the current fiscal year — only revenue collected during the next fiscal year and thereafter. But that may change, as we'll explain.

Going back to Prop CC's premise, we have no qualms about letting voters decide if they would prefer to forgo nominal refunds and let the state use the money for some long overdue societal needs. Indeed, it seems odd to be refunding money when transportation and education are severely underfunded.

Proposition CC would direct excess revenues — estimated to be $652 million in the coming two years — in equal thirds to K-12, transportation and higher education. That's about $215 million each for things that poll high as taxpayer priorities.

Unfortunately, the way Prop CC is currently written offers no guarantee that the money will go where the ballot measure says it will.

As we see it, there are three distinct problems with Proposition CC. First, the cap repeal is permanent. More on this momentarily.

Second, it's a statutory change, which means lawmakers can amend the measure if it's enacted. Future legislatures could decide that education and transportation are no longer priorities. But the cap repeal is permanent, remember? So there's no going back if taxpayers don't like what lawmakers are doing with the extra money they're keeping.

Third, there's no predictability. One year the extra money could amount to $65 million. The next zero. The next $400 million. How could lawmakers make long-term commitments to improve teacher pay or fund transportation projects with those kind of fluctuations? Besides, money is fungible in the Legislature. Let's say higher education is in line to get an extra $215 million next year. Lawmakers could simply short that line item by $215 million and use the Prop CC money to backfill the allocation. That's $215 million that can be spent elsewhere.

Proposition CC offers too many opportunities to deviate from what voters are being asked. Perhaps that's why former Gov. Bill Owens, who supported a five-year TABOR timeout in 2005, calls Prop CC "a permanent blank check." Owens is on the advisory board of the issue committee "No on CC" which includes Mesa County Commissioner Rose Pugliese.

We've long advocated for some kind of TABOR overhaul that would preserve voter approval of tax measures but correct some of its flaws, like the formula used to determine revenue limits or TABOR's insidious ratchet effect. Prop CC doesn't address TABOR's systemic shortcomings. All it does is ask voters whether they trust the Legislature to put surplus revenues to a higher and better use than refunds.

That's not a ridiculous question — provided there's some accountability. Proposition CC would be better if it had a sunset provision and tight guardrails that ensure surplus revenue supplements spending on transportation and education.

As it stands, Gov. Jared Polis is considering calling a special session to amend Proposition CC, in part to include the 2018-19 budget year and its $575 million bonanza. But it could also change from a permanent elimination of the TABOR tax refunds to a temporary one that lasts 10 or 15 years. (Our suggestion: Make it three to five years) Most Republican lawmakers aren't interested in a special session, but a handful have floated the idea of pairing a TABOR timeout with an income tax rate cut.

We'll revisit this issue once we know for certain whether Prop CC will change or proceed as it's currently proposed.

Recommended for you