REUTERS/Alessandro Bianchi

Florida's medical marijuana ballot measure, Amendment 2, came up short Tuesday, getting "only" 58 percent of the vote, not the 60 required to pass. But it may have motivated more young voters to turn out this year, according to preliminary exit poll data reported by NBC News. The exit poll shows 18-29 year-olds making up 14 percent of the electorate this year, compared to only 8 percent of the 2010 electorate. Seniors account for the bulk of that difference -- their share fell from 35 percent of the electorate in 2010 to 25 percent today.

fl-exit

Overall, the preliminary exit poll data shows that 61 percent of Florida voters approved of the medical marijuana amendment, which requires 60 percent support to pass. That one-point threshold is well within the poll's margin of error, meaning the measure will likely come right down to the wire.

The exit poll data shows greater than 60 percent support among Floridians of all age categories except for seniors, only 40 percent of whom backed the measure. Since seniors make up a quarter of the electorate, this difference could be crucial.

fl-exit-2

The data also show a significant gap in support between single Floridians - 73 percent of whom backed the amendment - and married Flordians, who only gave the measure 53 percent support. This suggests that marijuana supporters might need to strengthen their pitch to parents worried about potential marijuana use among their kids.

Opponents of Amendment 2 made concerns about youth use a cornerstone of their messaging. A  considerable body of research shows that medical marijuana measures do not lead to increases in teen marijuana use.

Currently with 71 percent of precincts reporting the medical marijuana amendment is showing 57 percent support, a sold majority but less than the 60 percent threshold required for passage.