Updated 2:40 p.m. | New Jersey Gov. Chris Christie set the special election to replace the late Sen. Frank R. Lautenberg for Oct. 16, with a special primary to elect nominees on Aug. 13.

At a news conference announcing the special-election process, the governor said he has not decided whom to appoint to hold the seat for the next four months until someone is elected.

The decision to hold the election this year sets up a likely Democratic primary clash between Newark Mayor Cory Booker and Rep. Frank Pallone Jr. The winner will likely be heavily favored in the general election, though the odd timing of the election and the quality of the eventual GOP nominee will no doubt be consequential.

The election law statute is vague enough that Christie could have appointed someone to hold the seat until November 2014, though Democrats made it clear on Monday that they would likely challenge that in court.

According to Christie, the decision to hold the election in October allowed for nominees to be selected through primaries and for voters to choose a new senator as soon as possible.

“This is about guaranteeing the people of New Jersey both a choice and a voice in the process and the representation that they deserve in Washington,” Christie said.

Republicans in the state speculated on Monday that Christie, who is up for re-election in November, would do what he could to avoid sharing a ballot with the Senate special election.

That would invite outside spending, likely increase Democratic turnout and ultimately affect his margin of victory. For now, Christie appears headed for an easy win against an underfunded Democrat.

However, his decision not to hold the elections concurrently could hurt Republicans’ chances of winning the Senate seat, since Christie won’t lead the ticket. It also comes at a significant financial cost, which Christie said the state will cover.

Despite speculation about his motives for holding the election in October, Christie said several times that the decision was not about politics.

“I want to have an elected senator as soon as possible,” Christie said. “There is no political purpose to this. The political purpose is to give the people a voice.”

Update 2:40 p.m.

Democrats in the state quickly criticized Christie for the move. Assembly Speaker Sheila Oliver said in a statement that Christie “has chosen to put partisan politics and his self-interest first” by not setting the special for November.

National Democrats said in a statement that the timing would hurt Republicans’ chances.