New Jersey Gov. Chris Christie (R) isn't taking any chances.

Riding high as polls continue to show he is a strong favorite to win reelection and one of the country's most popular governors, Christie's campaign has taken an aggressive early stance against underdog opponent and Democratic state Sen. Barbara Buono.

(Lucas Jackson/Reuters) (Lucas Jackson/Reuters)

Christie has unleashed multiple negative ads against Buono, including a rough spot this week tying her to embattled former governor Jon Corzine, the Democrat Christie unseated in 2009.

With the campaign kicking into gear (the primary is June 4), Buono has also quickly gone after Christie. Her first TV ad of the campaign sought to ding Christie's economic record.

The fact of the matter is that as popular as Christie is, he is running in a very blue state where no Republican running statewide is ever a sure thing. He's raised heaps of cash, and he is putting it to use, defining his opponent early. It's clear that Christie's not going to be passive this cycle, even as the consensus is that he won't face competitive race (New Jersey is not on our list of the cycle's 15 most competitive contests.)

Christie's widely praised response to Hurricane Sandy will surface again next week, when President Obama returns to the Garden State to tour the recovery process with the Republican governor. The first time around, the Christie/Obama photo-op didn't go over so well with some Republicans outside New Jersey. But inside the Garden State, it was exactly the kind of bipartisan, problem-solver posture voters like to see. Christie included footage of his Sandy response in his first TV ad.

Most of the political world has inked Christie in for a second term. And all indications are he is the clear favorite. But what's grown clear in recent weeks is that Christie's campaign isn't sitting back.

And now, to the Line!

(A reminder that the races below are ordered according to the likelihood they will result in a change of parties, with No. 1 being the most likely.)

15. Minnesota (Democratic-controlled): Minnesota Republicans are having a tough time recruiting proven vote-getters for the two big statewide races this year, but at the very least, Gov. Mark Dayton (D) is hardly bulletproof. A new poll showed his favorable rating dropping to 49 percent, with 47 percent unfavorable. His split was 53/39 in January. But Dayton still leads the two declared (and largely unknown) Republicans – businessman Scott Honour and Hennepin County Commissioner Jeff Johnson – by 18 points apiece. (Previous ranking: N/A)

14. Arizona (Republican-controlled): We could be looking at contested primaries on both sides in the Grand Canyon State. So far, former Clinton White House aide Fred DuVal is the biggest name in Democratic field, but he might get company from state Rep. Chad Campbell. If Gov. Jan Brewer (R) opts against challenging the term limit imposed by the state Constitution (an idea that picked up some buzz late last year but has seemed like more of a real long shot lately), look for a competitive GOP field to replace her. Former surgeon general Richard Carmona would have been a blue chip recruit for Democrats. In his absence, Republicans start with a clear edge in this race even before the nominees are known in this red state. (Previous ranking: 14)

13. Wisconsin (R): It's felt lately like there has been more chatter about what Gov. Scott Walker (R) will do in 2016 than 2014. He's writing a book and further fueled the 2016 presidential buzz surrounding him with a trip to Iowa this week. Walker's not invincible in his reelection bid next year, but Democrats need to find a proven candidate for this race before they can talk seriously about unseating him. And so far, they haven't done that. (Previous ranking: 13)

12. Connecticut (D): The rematch between Gov. Dan Malloy (D) and Republican former ambassador to Ireland Tom Foley has thus far been pretty quiet. Foley gets points for losing by slightly more than 6,000 votes in 2010, but that was a good GOP year, this is a Democratic state, and Malloy is a modestly popular incumbent, which means the Democrat is the favorite. (Previous ranking: 12)

11. Massachusetts (D): Rep. Michael Capuano (D) said recently that he is closer to making a decision about whether to run. With Attorney General Martha Coakley (D) sounding like she's not interested, a long list of Democrats are looking at the race. On the Republican side, the focus continues to be on 2010 candidate Charlie Baker and former senator Scott Brown, who has kept the political world guessing about his next move.  (Previous ranking: 11)

10. Ohio (R): Gov. John Kasich's (R) numbers have held pretty steady since he has turned around his once awful public image. Cuyahoga County Executive Ed FitzGerald has ginned up Democratic enthusiasm, and he looks to be the Kasich opponent-in-waiting right now. Ohio's economic rebound should help Kasich's chances. (Previous ranking: 10)

9. Illinois (D): We’re still waiting on Attorney General Lisa Madigan (D) to make a decision about challenging Gov. Pat Quinn (D) in the primary. If she runs, she’s the favorite in the primary and the general election. The other x-factor in the Democratic primary is former White House chief of staff Bill Daley. If the popular Madigan jumps in, you have to believe he is less likely to run. Daley suggested as much a couple weeks back. On the GOP side, businessman Bruce Rauner's exploratory committee has put up some solid fundraising numbers in a race that also includes State Sen. Kirk Dillard. (Previous ranking: 9)

8. South Carolina (R): For all the initial hype around Gov. Nikki Haley (R), many outside the Palmetto State overlook her tough spell as governor. As Politico noted recently, Haley has battled her own party, and a hacking scandal that revealed taxpayers’ information and high unemployment (though it's worth noting that's dropped significantly in recent months). State Sen. Vincent Sheheen is back for a rematch after losing by less than five points in a good GOP year in 2010. (Previous ranking: 8)

7. Virginia (R): It’s starting to look more and more like Attorney General Ken Cuccinelli (R) is the favorite here – at least to our eyes. Former DNC chairman Terry McAuliffe, quite simply, didn’t run a good primary campaign in 2009, and so far there are concerns that he hasn't gotten much better. There’s plenty of chatter about new GOP lieutenant governor nominee E.W. Jackson’s totally unhelpful past statements, but Jackson’s race is separate from Cuccinelli’s, and there is precedence for Virginia voters splitting their tickets. (Previous ranking: 6)

6. Michigan (R): Gov. Rick Snyder (R) is clearly vulnerable, and Democrats appear to have found a candidate to run against him in former congressman Mark Schauer, who has been looking closely at a run. Other potential Democratic candidates have voiced support for Schauer, suggesting that his road to the nomination would be pretty clear. It will be interesting to see what type of campaign Snyder runs. He campaigned as "one tough nerd" in 2010, but Democrats are now eager to paint him in partisan stripes after making Michigan a "right to work state." How much Snyder tacks to the middle and how much he seeks to gin up the conservative base will offer hints about where he thinks his path to victory lies. (Previous ranking: 7)

5. Pennsylvania (R): Gov. Tom Corbett’s (R) curious decision to joke about the lack of Latinos on his staff probably doesn’t help. Democrats think Rep. Allyson Schwartz (D) is the real deal, and she got the backing of Democratic women’s group EMILY’s List this week. But she wont get a clear path to the nomination, with many others eyeing the prize. She did get a break, however, when former congressman Joe Sestak (D) opted not to run and to instead focus on a 2016 rematch against Sen. Pat Toomey (R). (Previous ranking: 5)

4. Arkansas (D): Former congressman Mike Ross is one of the Democrats' top recruiting prizes this cycle, giving the party hope to hold onto a seat that once looked poised to turn red. Make no mistake, though: Former congressman Asa Hutchinson is just as solid a Republican recruit. Since both candidates have ties to Washington, the one that does a better job convincing voters he is "Arkansas first" stands to have an edge in this state race. (Previous ranking: 4)

3. Maine (R): Gov. Paul LePage (R) continues to rile up Democrats with his attention-grabbing antics. The latest: moving out of the State House because he wasn't allowed to put a TV display criticizing the legislature outside his office. With his approval rating hovering in the mid-thirties and a majority of Mainers disapproving of his performance, LePage might get lucky as another three-way race is shaping up. Independent Eliot Cutler is moving toward a bid and believes he can win a three-way contest. Democrats are vowing to field a candidate who can take on Cutler in LePage in what could be a repeat of 2010. Rep. Chellie Pingree is out, leaving Rep. Mike Michaud and former governor John Baldacci as likely candidates. (Previous ranking: 3)

 2. Rhode Island (Independent-controlled): Things continue to look bad for independent Gov. Lincoln Chafee, and he knows it. He's still thinking about becoming a Democrat, telling a reporter that it's hard to succeed without a “party apparatus as a natural defense.” But like LePage, Chafee may be saved by a three-way race: Moderate Party founder Ken Block is launching another bid. Allan Fung is looking like the top GOP candidate, while state Treasurer Gina Raimondo and Providence Mayor Angel Taveras are both potential Democratic contenders. (Previous ranking: 2)

1. Florida (R): We’ve still got Gov. Rick Scott (R) as our most vulnerable incumbent on this list. Sen. Bill Nelson (D) hasn’t totally ruled out a run, but he doesn’t sound like he’s going to run either. Which would leave former governor Charlie Crist (D), under his new party banner, as the presumptive Democratic nominee to try and reclaim his old office from his successor. (Previous ranking: 1)