The two polls may indicate why Booker released his first negative ad of the campaign on Tuesday, just over two weeks from Election Day. The ad, titled "Done," accuses Lonegan of being "too extreme for New Jersey," and features Booker declaring, "New Jersey, we're better than that."

The new survey, from Monmouth University, gives Booker a 13-point lead over Lonegan, taking 53 percent support to the Republican's 40 percent support among likely voters. That's similar to a Quinnipiac University poll released last week, in which Booker posted a 12-point lead.

Booker's lead has dropped substantially since mid-September, when one poll showed him leading his opponent by 26 percentage points.

And the Monmouth University survey gives clear evidence Lonegan's attacks on Booker, which have centered around his celebrity connections and the perception that the young Democratic star is focused more on raising his own profile than working for New Jersey, may be taking their toll.

A plurality of respondents, 45 percent, said they believe Booker wants to be a senator more for exposure on the national stage, rather than to serve the state. Thirty-five percent said they believe he's more concerned with the state.

Booker has, until this point, largely ignored Lonegan's attacks, and has spent portions of the election out of the state. His new ad is a pointed pivot to the negative as his support looks to be eroding in the final weeks of the campaign.

His new ad charges that Lonegan wants to privatize Social Security, shut down the government and ban abortion.

New Jersey is a deep-blue state, making those positions largely unpalatable for voters and Booker the heavy favorite to win on Oct. 16. 

The survey was conducted among 571 likely voters from Sept. 26-29 and has a margin of error of plus or minus 4.1 percentage points.

--This post was updated at 6:03 p.m.