When Amendment 64 was passed last November and signed into law by Governor John Hickenlooper the following month, most Coloradans figured it was a done deal -- unless the federal government decided to oppose it, that is. But no: Last night, Senator John Morse, seen here, and a slew of colleagues came within a whisper of passing a bill, SCR13-003, that would have allowed the state's voters to repeal the retail portion of the law if taxes to pay for it aren't approved this November. See the bill and learn more about its brief life below.

As we've reported, the Taxpayers Bill of Rights, shorthanded as TABOR, requires a vote to approve tax increases. Hence, House Bill 13-1318 was designed to set rates to be considered in this November's election. An excise tax of 15 percent was envisioned in A64's language, but a sales tax of up to 15 percent not sketched out in the amendment has also been pushed.

Just over a week ago, Amendment 64 proponent Mason Tvert came forward to decry a repeal effort that he associated with Smart Colorado, a group that's been pushing for the maximum number of restrictions possible on A64.

"According to lawmakers at the State Capitol, Smart Colorado has been floating the idea of referring a measure to voters that would repeal Amendment 64 if a special sales tax of 15 percent does not pass," Tvert told us for an April 26 post, "This amounts to extortion of the voters. They're being told they must approve a higher tax level proposed by legislators or otherwise the constitutional amendment they adopted in November would be repealed."

Smart Colorado spokesman Eric Anderson countered that his group hadn't conceived the repeal effort but found value in it. His statement reads:

Amendment 64 backers sold the ballot issue to Colorado voters as a way to pay for state priorities like education but increasingly it's looking like it could be a net drain on the state budget. Amendment 64 raised the possibility of new taxes on marijuana but didn't enact them. If voters don't now approve new taxes on marijuana, Colorado's budget will take a major hit and Amendment 64 will have exactly the opposite effect from what was promised to voters.

In the following days, attorney Ed Ramey, who had been consulted on the repeal question, offered his opinion that such a measure would be unconstitutional. We've previously reported that his main point involved rules calling for proposed constitutional amendments to be considered only during elections that fall during even-numbered years, with elections in odd-numbered years featuring questions concerning "issues of government financing, spending, and taxation."

For that reason, Ramey sees it as logical that a repeal could only go forward during an even-numbered year, with 2014 presumably being the next opportunity to strike the amendment from the books. Should such an attempt be made in 2013 instead, Ramey sees it as "possible that the courts could invalidate the repeal...while sustaining the vote on the tax component." That could potentially leave Amendment 64 intact but kill taxes on marijuana entirely.

Nonetheless, legislators remain so freaked out by the prospect of voters going to the polls in November and rejecting taxes to pay for Amendment 64 implementation -- this despite a poll commissioned by proponents that showed support at 77 percent -- that the repeal effort not only stayed alive, but gathered steam.

Continue for more about the Amendment 64 repeal effort, including photos, a video and the failed bill. The result, introduced last night, was SCR13-003. The entire bill is below, but its summary spells out the basics.

"The concurrent resolution submits two questions concerning marijuana to the voters of the state at the statewide election to be held in November of 2013," it begins. "If the voters approve the first question, the concurrent resolution will impose a state sales tax and a state excise tax on retail marijuana, legalized by section 16 of article XVIII of the state constitution."

That first question involves the excise and sales taxes, with both set at 15 percent. (The latter digit is controversial. A64 proponents and many legislators prefer a 10 percent sales tax, thinking the odds of voters approving it are higher.) The summary later notes that "if the voters approve the first question, the state will be allowed to collect and spend any revenues generated by the retail marijuana excise and sales taxes as voter-approved revenue changes."

What if the voters don't approve the first question, but bless question number two -- the one concerning repeal? Then, the bill states, "the concurrent resolution will suspend all provisions of section 16 of article XVIII of the state constitution relating to the regulation of marijuana until such time as voters approve the imposition of new state taxes or increases in state tax rates sufficient to fund the estimated costs of state regulation of marijuana."

As noted by 9News, SCR13-003 was backed by some heavy hitters, including Majority Leader John Morse and 23 other Senators. But frantic testimony from A64 proponents, including Betty Aldworth, was accompanied by push-back from members of the House and threats of a filibuster that threatened to derail the rest of the legislative session.

After consultation, supporters of SCR13-003 raised the white flag around 9:30 p.m. last night.

At this point, the repeal measure appears to be dead for this legislative session -- and the next one doesn't start until early next year, well after this November's election. As such, there will be tremendous pressure for voters to approve the taxes to pay for Amendment 64.

If they don't, the A64 implementation costs will have to come from other sources until the legislators return. Under that scenario, a measure to repeal Amendment 64 would almost certainly gain traction, presumably running neck and neck with additional tax proposals that might somehow win the favor of Colorado voters.

Whew! Look below to see the 9News report, followed by the text of SCR13-003.

Editor's note: The original version of this post stated that the repeal would have suspended the entire law, not just the retail section of it. We've corrected this reference and regret the error.

More from our Marijuana archive: "Marijuana: Barack Obama says no to legalizing drugs -- but what's that mean for Colorado?"