The poll of 614 likely voters found that 48 percent of respondents support the measure, while 43 percent oppose it. A poll last month found a wider lead for Amendment 64, with 51 percent in support and 40 percent opposed. Both polls have a 4-percentage-point margin of error.
The most noticeable swing in the new poll, taken Tuesday and Wednesday for The Denver Post by SurveyUSA, came among women. The previous poll showed the measure succeeding with women 49 percent to 39 percent. The new poll, however, shows women opposed 48 percent to 40 percent.
Men continue to support the measure, as do young voters and those ages 50 to 64. But a slender lead among voters ages 35 to 49 has turned into a 4-point deficit, while voters 65 and older disapprove of the measure by a wider margin.
The poll comes as the campaigns for and against the measure have been heating up, with both sides announcing a series of endorsements.
Read more of John Ingold's story in the Denver Post.
(Copyright 2012 The Denver Post)