Rep. John Tierney (D-Mass.) is running slightly behind Republican challenger Richard Tisei, a new poll released Monday shows. It's the latest sign of trouble for the incumbent, whose wife's family's legal woes have complicated his reelection bid. 

A new Boston Globe poll shows Tisei, a former state senator, leading Tierney 37 percent to 31 percent among likely voters. Fully 30 percent of likely voters are undecided, suggesting room for either candidate to seize the advantage in this contest down the stretch. The poll's margin of error is +/- 5.1 percentage points. 

A Republican poll recently conducted for YG Action Fund also showed Tierney running behind Tisei by single digits. YG Action is a super PAC run by former aides to House Majority Leader Eric Cantor (Va.) that has been supporting Tisei. 

Tierney's wife's family has faced legal trouble involving a gambling operation. And while Tierney himself has never been charged with any wrongdoing, the association has dinged his image. In the Globe poll, his favorability is under water, with just 32 percent saying they had a favorable opinion of the congressman, while 43 percent said they had an unfavorable view. What's more, only about half of Democrats said they viewed him favorably. 

It's been a rough stretch for Tierney. Last month, the Democratic super PAC Majority PAC pulled back TV ads that could have benefited him. While the group said the move should not reflect on its confidence in Tierney's ability to win, it wasn't exactly the news the congressman was looking for. 

A Tisei win would be a historic feat for at least a couple of reasons. First, he'd be the first Republican to win a House seat in the Bay State in 16 years. Second, Tisei is openly gay, and as the Globe noted this morning, would be the first openly gay Republican congressman to reveal his sexual orientation before he was elected.

(For more on Tisei, Tierney and the 6th District race, check out The Post's Paul Kane's dispatch from Wakefield.)

Republicans have slammed Tierney over his family's legal troubles in ads, and it's clearly beginning to take a toll. Tisei, notably, didn't bring up the issue at the candidates' first debate last month

The Democratic playbook against Tisei involves casting him as too far to the right for the district. At the debate, Tierney mentioned more than once that Tisei has called the Tea Party a “godsend," the Globe reported. 

For Tisei, the goal is to cut a moderate profile and present himself as an acceptable alternative to Tierney. So far, he's holding his own.