Two weeks from today, New Jersey voters will decide who takes over the U.S. Senate seat of the late Frank Lautenberg. The race for that seat is tighter than originally predicted by political pundits.

Special Senate Election candidates Democrat Cory Booker (L) and Republican Steve Lonegan (Facebook)

Democrat Cory Booker holds a 13-point lead over Republican Steve Lonegan, according to a new Monmouth University poll. Booker's lead was 16 points in June and August.

"While Cory Booker's lead is relatively sizable, many voters have doubts about his motives in seeking this seat," said Patrick Murray, director of the Monmouth University Polling Institute.

When asked about Booker's main reason for participating in the election, most voters (45 percent) said Booker is more interested in gaining the national spotlight. Thirty-five percent said Booker is mostly focused on serving New Jersey.

Booker's favorable rating among voters declined seven points since June, with 54 percent of likely voters offering a positive opinion of Newark's mayor. His unfavorable rating jumped to 28 percent, up 13 points since June.

"It's possible that Steve Lonegan's attacks have caused many voters to reconsider their opinion of Booker, even if they don't change their vote," Murray said.

Voter awareness has increased for Lonegan over the past few months. His favorable rating has held fairly steady, between 31 and 35 percent, while his unfavorable rating increased by eight points. Thirty-six percent of voters said they know a great deal about where Lonegan stands on the issues that are important to them.

According to Murray, the October 16 election may end up producing the lowest turnout ever for a statewide race that includes a U.S. Senate seat at the top of the ticket.

If given the choice of voting in only one election - the special Senate race or the gubernatorial race in November - 29 percent of voters said they would head to the polls to decide New Jersey's next Senator.