Activist Bob Massie dropped out of the Democratic race to take on Sen. Scott Brown (R-Mass.) on Friday, noting in a statement to supporters that “the dynamics of the race have shifted so profoundly that I can no longer see a path for me to win the Democratic nomination.”

Massie became the second Democratic candidate to end his bid after Harvard University professor Elizabeth Warren’s entrance into the race last month. Warren, who has significant support from the Democratic establishment in Boston and Washington, D.C., topped recent polls of Democratic primary voters. Newton Mayor Setti Warren also recently ended his campaign, citing a similar rationale.

City Year co-founder Alan Khazei, who lost a primary bid for the 2010 special election, remains the other serious contender in Democratic primary. The Boston Globe reported that Khazei raised $365,000 this quarter.

Roll Call rates the Massachusetts Senate race as a Tossup.