Gov. Chris Christie announced Tuesday that he has ordered a special election this fall for choosing a successor to the late U.S. Sen. Frank Lautenberg.

Christie issued a writ setting a special primary for Aug. 13 and a special election for Oct. 16 — less than three weeks before Election Day, Nov. 5.

At a press conference, Christie acknowledged that he could simply appoint a stand-in for the balance of Lautenberg’s term, which ends next year. The U.S. Constitution empowers states to decide how to fill Senate vacancies, and New Jersey is one of 36 states that allows the governor to name a replacement for the balance of a term.

"But I firmly believe that the decisions that need to be made in Washington are too great to be determined by an appointee for a period of 18 months," he said, citing immigration reform, tax reform and budgetary issues. "We have to move swiftly to fill this seat and ensure that there is a primary and general election as soon as possible."

The dates given were the soonest allowable by law. A statute, N.J.S.A. 19:27-6, requires a minimum of 70 days between the writ and the special primary and a minimum of 64 days between the primary and the special election.

Christie said a special election was needed because the statute would otherwise preclude putting the choice to the voters until November 2014.

Christie announced on Thursday his appointment of Attorney General Jeffrey Chiesa as a temporary replacement until the special election. With Chiesa, a Republican, the GOP will control 46 Senate seats and the Democrats 52. Two Independents join the Democrats in caucus.

Lautenberg, who died on Monday, announced in February that he would not seek re-election, and several Democrats had expressed interest or at least had their names mentioned.

Newark Mayor Cory Booker has already filed paperwork with the Federal Election Commission. Others considering a run are Reps. Frank Pallone and Rush Holt, state Senate President Stephen Sweeney and state Assembly Speaker Sheila Oliver.

The elections will be paid for by the state and administered by the secretary of state’s office. The Office of Legislative Services estimated in a recent opinion that the special primary and special election would cost about $12 million each.

State Assemblyman John Wisniewski, chairman of the New Jersey Democratic State Committee, calls Christie’s decision "entirely self-serving" and "a thinly veiled political move to try to separate the … senatorial race from his re-election."

Contrary to Christie’s interpretation of state election law, the Legislature did not contemplate having a costly special election three weeks before a scheduled general election, Wisniewski adds.

Democratic leaders are reviewing their options, he says. "It may be litigation; it may not."

Wisniewski says the move shows that Christie is concerned about higher voter turnout if the Senate vote were held on Nov. 5.

Squeezing in the special election before Nov. 5 also could have the effect of dividing Democratic resources between the Senate and gubernatorial races. "There’s not an unlimited amount of money," Wisniewski says. "There will be some people who are contributors who will have to figure out where to put their money. Somebody will end up collecting fewer contributions because of this."

Christie drew fire from other Democrats on Tuesday, including state Sen. Richard Codey, a former acting governor. In a statement, Codey called the decision "mind boggling in every rational way."

Codey said, "Instead of holding an expensive special election that tries to protect the governor’s political vulnerabilities, the voters should have the opportunity to have their say in the regular election in November."

Christie during his news conference denied that there was any political purpose for the timing of the special election. He said that because Lautenberg’s death came before the June 4 primary, having the election this Nov. 5 was "not an option."

N.J.S.A. 19:27-6 provides that a vacancy must be filled at the next general election unless it arises less than 70 days before the next primary, in which case it must go to the second succeeding election, meaning November 2014.

Spokesman Michael Drewniak did not return a call seeking comment on the Democrats’ criticisms.