Rabbe said there's evidence that late deciders are breaking 2-to-1 in favor, but they might not be as committed to voting as those who made up their minds early.
Kimberly Raffensparger, 50, a white Democrat from Glyndon, said that in recent weeks she has moved from undecided to supporting the measure. What she's learned about the eligibility requirements for in-state tuition has convinced her the program would not be a giveaway to immigrants.
"It seems like they have to jump through a number of hoops. I'm beginning to lean toward it," she said. "You have to prove you've been contributing toward the system and to me that's important."
Diane Aull, 59, of Perry Hall has moved from undecided to leaning against.
"If they're illegal, I say no," said Aull, a Republican. "There are too many people here in Maryland who need help."
The state's new congressional map has been criticized by Republicans and some Democrats as flagrantly gerrymandered, while the governor and General Assembly leaders describe it as fair and point out it has withstood legal challenges.
The map is an arcane question on an already busy ballot. Though it is believed to provide an advantage for Democrats in this mostly Democratic state, Raabe believes that there could be bad news for the party leaders in Annapolis who redrew it last year.
"It is close," Raabe said. "I'd be a little nervous if I were a supporter of this map."
The telephone survey of 801 likely voters was conducted by OpinionWorks, an Annapolis-based polling firm, from Oct. 20 to Oct. 23. The margin of error is plus or minus 3.5 percentage points.