A new poll conducted for a Democratic super PAC shows Seth Moulton, the Democrat who ousted Rep. John Tierney in a Sept. 9 primary, holding a 10-point lead over his Republican opponent in the general election in Massachusetts' 6th Congressional District.

Moulton leads Republican former state Sen. Richard Tisei 43 percent to 33 percent, according to a poll by the Democratic firm Garin-Hart-Yang Research Group, conducted for House Majority PAC. Third-party candidate Chris Stockwell received 11 percent in the poll, and 13 percent were undecided. The poll surveyed 400 likely voters from Sept. 24 to 27, and has a margin of error of plus or minus 5 percentage points.

Partisan polls should be taken with a grain of salt, and several other polls conducted in late September have gotten mixed results. An Emerson College automated poll, conducted Sept. 26-29, showed Tisei leading within the margin of error, 41 percent to 39 percent. A survey by the Tarrance Group, a Republican pollster, conducted for Tisei's campaign, also showed the candidates virtually tied, with Tisei holding a 1-point lead. But a WBUR poll conducted Sept. 22-24 showed Moulton with an 8-point advantage, leading 47 percent to 39 percent. Two automated Democratic polls conducted earlier in September showed Moulton with leads of 8 points and 18 points.

Tisei's campaign responded to the poll, saying it expects a close race in the moderate district.

"We've been saying since Day 1 that this election will be competitive all the way until November 4," said campaign spokesman Charlie Szold. "Richard lives and works on Main Street, and will fight everyday for the people of the 6th District."

This poll is especially positive for Moulton considering that Stockwell is expected to pull more votes from him than from Tisei, so if Stockwell receives less than the 11 percent he received in this poll, Moulton could gain even more of an advantage. Third-party candidates rarely do as well on Election Day as they do in the polls.

Tierney was expected to have another tough race against Tierney, but many Democrats expect Moulton to be a better general-election candidate. Tierney beat Tisei by only a few thousand votes in 2012, and has been hampered by bad press since his wife and brother-in-law were charged with running an illegal offshore gambling business—which Tierney has maintained he was not involved in.

Tierney would have been one of Republicans' top targets this cycle, but the moderate district is still seen as a possible pickup opportunity for Republicans. Since winning the primary, Moulton's challenge has been to attract support from potentially disaffected Democrats who voted for Tierney.

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