Mass. Senate race tightens as Moulton polls 5 points behind Markey

• That marks the closest margin yet in the Democratic primary.

State of play: The race has narrowed dramatically since earlier this year, when previous surveys showed Markey leading by nearly 20 points.

• Unenrolled voters are behind the shift, favoring Moulton 38% to 32% for Markey.
• Registered Democrats remain Markey's firewall. He maintains a 13-point advantage there.
• 29% of voters say they're undecided, leaving the race wide open.

Of note: Emerson's poll subset of 451 likely Democratic primary voters produced a +/- 4.5% margin of error.

What's next: Moulton's momentum among independents will be the metric to watch as the campaign enters high gear this summer.

• The primary is on Sept. 1.