A poll conducted for a coalition of environmental and conservation organizations found that Rep. Martin Heinrich (D) has expanded his lead over former Rep. Heather Wilson (R) in the race for New Mexico’s open Senate seat.

A memo from California-based Democratic polling firm FM3 showed Heinrich leading 50 percent to 41 percent, with 9 percent undecided. The poll was conducted Aug. 5-7 among 502 likely voters with a 4.4-point margin of error.

The firm’s previous poll, taken in May, had Heinrich ahead 48 percent to 45 percent. Since then, the memo noted, Wilson’s unfavorable rating has increased to 42 percent and Heinrich has taken a significant lead among independents and expanded his lead among women.

Heinrich and Wilson are running for the seat of retiring Sen. Jeff Bingaman (D). Roll Call rates the race as a Tossup.