It's been a busy week in New Jersey politics. Sen. Frank Lautenberg's death set into motion a series of events culminating in an August primary and October special election to fill his seat.

Newark Mayor Cory Booker. (Julio Cortez/AP) Newark Mayor Cory Booker. (Julio Cortez/AP)

So, who has the upper hand? And what are the most important variables to keep an eye on as the race moves forward? Below we run down the biggest knowns and unknowns. Agree/disagree? The comments section awaits your input!

Here's what we know:

1) Cory Booker is still the clear favorite. But... It's clear that Newark Mayor Cory Booker (D) is the candidate to beat, in both the Democratic primary and the overall election. Booker's been laying groundwork for months, has name ID like no other Democrat in the mix, and will be able to raise big, big bucks. All of which matters in a populous and expensive state like New Jersey.

But Booker, who has started collecting signatures to appear on the special election ballot, has got to be at least a bit more nervous than he was before this week. The August primary could attract several contenders from the House delegation (Rep. Rush Holt will run, and party strategists expect Rep. Frank Pallone to make a bid, too). A crowded field, short campaign window and the potential for a very low turnout summer election are new variables that didn't exist before this week. Indeed, a vote-split among other candidates could help Booker. But, depending on what the Democratic field looks like, a roster of well-funded contenders could mean he takes more hits, too. Booker's got the upper hand, but he faces a whole new campaign right now.

2) It's a tough climb for Republicans. The prospect of having a GOP appointee take office until November of 2014 raised Republican hopes of winning a Senate seat in deep blue New Jersey earlier this week -- something they have not done in decades. A 2013 election, on the other hand, was not welcome news for Senate Republicans. The GOP is hoping a messy Democratic primary will produce a wounded nominee that will open the door for a general election upset. It could happen. But at this point, a Democratic victory looks much likelier.

3) The filing deadline is fast approaching. The clock is ticking for candidates mulling a run, with a Monday filing deadline right around the corner. Candidates will need to obtain 1,000 signatures, which shouldn't be a big deal for the major players. But it means it's now or never for potential candidates who are on the fence. The quick turnaround will force pols to decide swiftly.

And what we don't know:

1) How big the Democratic field will get: In addition to Booker, Pallone and Holt, how many others will get in the race? And where will the fault lines be in the primary? Geography could be major factor if someone from South Jersey gets in the race. Booker and Pallone are from North Jersey, while Holt hails from the central part of the state.

2) Who the Republican nominee will be. We don't know who the Democratic nominee will be either, but there is more clarity at the top of the field on that side. Christie on Thursday appointed state Attorney General Jeff Chiesa to serve as an replacement for Lautenberg. But he won't run in the special election. Who all on the GOP side will is an open question at this point.

Former Bogota mayor Steve Lonegan, a conservative, says he will run, but he's all by himself right now. Assembly Minority Leader Jon Bramnick said he is not interested in running. State Senate Minority Leader Thomas Kean Jr. also has said he has no interest. And Lt. Gov. Kim Guadagno and state senator and 2012 nominee Joe Kyrillos are reportedly unlikely to make bids.

2) What primary turnout will look like. Aug. 13 is not an ideal time to hold an election if you are looking to attract many voters. With many people on vacation during the hottest month of the summer, turnout could be very low. Under such a scenario, candidates with the most loyal bases and best turnout operations would have an advantage.

Updated at 4:22 p.m. with Chiesa's appointment and the latest on the GOP field.