There are many nightmare scenarios out there about what could happen on Election Day. An Electoral College tie. An electronic voting glitch in a state that has moved to a new voting system. A call for a recount in a state like Ohio that still uses punch cards. A disruption by a terrorist group. Thinking about such scenarios is fair game after the 2000 debacle, in which the outcome was decided in mid-December after intervention by the U.S. Supreme Court.

One scenario that deserves more attention involves Colorado. On Nov. 2, Coloradans will be doing more than voting for president. They also will consider Amendment 36, a voter initiative that, if passed, will change the way Colorado’s nine electoral votes are allocated.

Most states, including Colorado, award all of the state’s electoral votes to whichever presidential candidate obtains the greatest number of votes there. Amendment 36, if passed, would divide Colorado’s electoral college votes proportionately, depending on how many votes each candidate wins. What’s more, it declares unambiguously that “the popular proportional selection for presidential election is intended to apply retroactively and thus determine the manner in which our state’s presidential electors are chosen and our state’s electoral votes are cast for the general election of 2004.”

In other words, if George W. Bush narrowly gains more votes than John Kerry (right now, things look like a toss-up), Bush could end up with only four or five electoral votes rather than nine.

Put aside for a moment the question of whether this is a desirable new law. And put aside the question of whether it will help Kerry or Bush.

The more important point is this: With such a close race nationally, the results of the nationwide election could well turn on a judicial determination whether Amendment 36 applies (or on exactly how it applies, if there are ambiguities). Bush won the last election, don’t forget, by only five electoral votes.

That is where the Colorado nightmare could begin.

We can start with the simplest way that things can go wrong: The vote on Amendment 36 could be very close, and there might need to be a recount of votes, throwing the entire national election into dispute.

Second, opponents of Amendment 36 could go to court claiming that it is unfair and unlawful to apply Amendment 36 retroactively to this election. This argument seems doubtful because there is no unfair surprise here.

The most interesting and trickiest legal question has to do with Article II of the Constitution, which allows each state Legislature to set the rules under which electors are chosen and allocated. When the U.S. Supreme Court was considering the 2000 Florida controversy, supporters of Bush argued that the Florida Supreme Court, in extending the deadline for Al Gore to contest the election and later by ordering a recount, had violated Article II. The argument was that the court had usurped the Legislature’s power.

In its first decision in the Florida controversy, the Supreme Court suggested that such an argument might be plausible, though it failed to decide the issue conclusively. In the second decision, Bush v. Gore, three justices — Chief Justice William Rehnquist and justices Antonin Scalia and Clarence Thomas — embraced the view that the Florida Supreme Court’s actions violated Article II. How will the Supreme Court handle the issue if it arises again?

A 1916 Supreme Court case suggests the Colorado initiative complies with Article II, but Rehnquist, Scalia and Thomas recently cast doubts on this precedent as applied to Colorado.

Would at least two other justices be willing to consider finding Amendment 36 a violation of Article II, in the context of deciding yet another presidential election? The court’s decision to stay out of a similar controversy in New Jersey two years ago is a hopeful sign that they wouldn’t.

Still, with such high stakes and uncertain law, we can keep the Colorado scenario within the realm of possible Election Day disasters in the making.

Richard L. Hasen, a professor at Loyola Law School in Los Angeles, is author of “The Supreme Court and Election Law.”