A November Colorado ballot measure would ban all borrowing by the state and severely restrict it at the municipal level, making Colorado the only state whose agencies would be unable to issue debt, municipal experts say. Nor would state agencies be able to turn to banks. The measure—an amendment to the state constitution requiring a simple majority to pass—was backed by 36% of voters surveyed in August by a Colorado pollster, even though both Republicans and Democrats have called it fiscal suicide. While that is well short of a majority, the prospect of passage has set off a rush to...