Four years ago, Marc Elrich and David Blair finished 77 votes apart in the race for Montgomery County executive. A poll released on Friday shows that — with the all-important Democratic primary just days away — the pair could be headed for another photo finish. According to Data for Progress, a San Francisco-based firm, Elrich and Blair are tied at 34%, with County Councilmember Hans Riemer at 20% and 11% undecided. Candidate Peter James, who ran for congress as a Republican in 2012, has one percent support. Early voting ended on Thursday and the primary is July 19.