That previous decision will likely fuel criticism from Democrats, who say Christie's decision to set the current special nearly a month prior to the upcoming gubernatorial and state legislative elections is a waste of taxpayer money for political gain.

Democrats had urged Christie to set the special election date for Nov. 5, ostensibly to save the state money. But they also stood to receive a potential boost in support for their gubernatorial nominee, Barbara Buono, who trails Christie by a large margin in polls.

Democrats privately hoped that a high-profile Senate candidate along the likes of Newark Mayor Cory Booker would boost turnout and at least narrow the gap Buono is likely to face in her own race. A potentially weak Republican Senate candidate could also drag down Christie's numbers.

But competing state statutes gave Christie wide discretion over when to set the date of the special election, with one suggesting it should take place this upcoming November. Another suggested the replacement should be elected during the already scheduled 2014 Senate election. Both gave Christie the option to set an alternate date, which he ultimately chose.

But in March 2012, Christie signed a writ of election that left Payne's seat vacant until it could be filled in the upcoming general election, in November 2012.

Special elections are rare in New Jersey precisely because of the cost, which some estimate could run as high as $24 million. Christie offered little explanation for his decision to depart from precedent, saying only that he wanted to let voters weigh in on the seat as soon as possible.

"I deem it advisable to have a special election. In fact, I deem it necessary," he said, arguing the costs of a special election "cannot be measured against the value" of giving voters as quick a vote as possible.

"I don't know what the cost is, and I quite frankly don't care," he later said.