Scott Brown's long-shot bid in the New Hampshire Senate race appears to be going in the wrong direction.

A new WMUR/University of New Hampshire poll released Tuesday shows Democratic incumbent Sen. Jeanne Shaheen doubling her lead over the Republican former Massachusetts senator with a little less than four months before Election Day. Shaheen leads Brown by 12 percentage points, 50 percent to 38 percent -- 6 points more than the lead she had in the April poll from WMUR/University of New Hampshire.

To make matters worse for Brown, who lost to Elizabeth Warren in Massachusetts in 2012, Shaheen's popularity is growing with Granite State voters. Fifty-seven percent of those surveyed have a favorable opinion of the job she is doing, compared with 29 percent who said they have an unfavorable opinion. Just 31 percent of New Hampshire adults said they have a favorable opinion of Brown, however, while 40 percent have an unfavorable opinion.

Shaheen's campaign touted the numbers in a press release by highlighting her challenger's unpopularity.

"This poll shows what Granite Staters know: Jeanne Shaheen puts New Hampshire first and her common sense leadership makes a difference for people here. She's got deep roots in New Hampshire, raised her family here and her record proves she shares our values," campaign manager Mike Vlacich said.

In some good news for the Republican, only 17 percent of likely voters say they have definitely decided whom to support in the race. A whopping 69 percent are still trying to decide, allowing Brown some potential room for improvement.

"So right now, with the dynamics that we have going on, she's in pretty good shape, but as we said, nobody is really paying attention to this race," said pollster Andy Smith of the University of New Hampshire Survey Center.

New Hampshire's Senate primary is scheduled for Sept. 9. Former Sen. Bob Smith and former state Sen. Jim Rubens -- who are also Republicans running for the nomination -- trail Shaheen by 23 points and 26 points, respectively, in potential matchups.