The popular first-term governor could, as is often the case in situations like these, choose to select a close ally from his own party as a replacement for Lautenberg. State law says the governor "may" appoint a replacement, and it's hard to see Christie leaving the seat vacant. A few obvious possibilities are state Sen. Tom Kean Jr., the party's 2006 Senate nominee; Lt. Gov. Kim Guadagno; and Joe Kyrillos, a close Christie ally whom the GOP nominated for the Senate in 2012.
Of course, it's possible -- though less likely -- that Christie would appoint a Democrat to the seat. He is campaigning as a bipartisan governor in a very blue state, after all. Tapping a Democrat would be seen as a major stroke of bipartisanship. Replacing a Democrat with a Democrat and then saying the voters should decide what happens next in November would no doubt be very well received by Democrats and moderates.
But such a move would be politically perilous for Christie and would run the risk of angering Republicans, the last thing Christie needs if he has any designs on running for president in 2016. He has already stoked some concern among conservatives by embracing President Obama in the aftermath of Hurricane Sandy.
Because Lautenberg had already announced he was not running for reelection in 2014, the Democratic race to replace him has been in full swing. Newark Mayor Cory Booker (D) has been actively exploring a bid and has been viewed as the clear frontrunner ahead of the regularly scheduled 2014 election. Rep. Frank Pallone (D) also has been considering a bid.
Booker had long been seen as a potential Christie opponent leading up to this year, but he opted to run for the Senate instead. Christie and Booker have a good relationship, which they have poked fun at over the years. If there is a Democrat whom Christie might be tempted to appoint, Booker would be that Democrat.
Christie will also have broad authority to set a special election for the seat. But when that will happen is unclear. Because of the high costs associated with holding an election, setting an election to fill the seat for Nov. 5, 2013 seems like the natural choice. New Jersey is already holding its off-year state elections at that time. Christie is running for his second term this year, and polls show he is a substantial favorite.
But New Jersey special election law is a somewhat murky, with two provisions that are difficult to square up. One rule states that if the vacancy occurs more than 70 days before the next general election (as it does in this case), then it will be filled in the next general election. Simple enough.
Another, however, reads that if the vacancy occurs less than 70 days before the primary -- this year's primary is set for June 4, so were are within that window -- the election wouldn't be held until 2014, unless Christie calls for an earlier special election.
On one hand, appointing a Republican replacement this year and affording that person more than a year to build a Senate record and a base would seem to work to the GOP's advantage. But running a GOP candidate alongside a popular Christie in 2013 might also represent Republicans' best chance at an unlikely win.
If there is a special election this year, it seems likely that Booker will be on the ballot, one way or the other. Even if Christie doesn't appoint him, he's already begun laying the groundwork for a Senate bid and would be an obvious choice for Democrats to nominate for the special election.
There is also the question of what a 2013 Senate election would do to Christie's own odds. If Booker is running for the Senate this fall, he will fire up a Democratic base that Christie's opponent, state Sen. Barbara Buono (D), could try to tap into herself.
In short, there are many variables at play.
This much is clear: Whoever wins the Senate seat this year (if there is an election) will have to turn around and immediately run for election again in 2014.
With Christie considered a strong favorite for reelection, it was looking to be a quiet year in New Jersey politics, at least in statewide races. But not now.
Updated at 3:26 p.m. with more details on New Jersey special election law