About halfway through the midterm election cycle, North Carolina is on pace to host the most expensive Senate race of 2014.

But the Tar Heel State shouldn’t necessarily get too comfortable in the top spot.

Democratic Sen. Kay Hagan’s re-election battle is one of at least four Senate contests where outside spending has already eclipsed the $2 million mark. The others include the re-election races of Sens. Mark Pryor, D-Ark., Mary L. Landrieu, D-La., and Mitch McConnell, R-Ky.

The potential for Republicans to win back the Senate majority, combined with the media-market makeup of the competitive landscape, has invited a superfluity of early spending. Republicans need a net gain of six seats next year, and most of the competitive races are for Democrat-held seats in less populous states.

“Given the president’s plummeting job approval ratings, there is growing optimism that Republicans can win back the Senate, and that’s why you’re seeing some very early spending in key U.S. Senate races,” GOP media consultant Erik Potholm said. “And Democrats, especially their vulnerable incumbents, are feeling that same pressure — that’s why Sens. Landrieu and Pryor are on the air.”

The major players in outside spending so far have been Americans for Prosperity, a GOP-aligned group underwritten by the Koch brothers, and Senate Majority PAC, whose primary goal is to keep Democrats in the majority. Both groups were also highly active in the 2012 elections and were able to ramp up their spending operations early this cycle.

North Carolina has some of the largest and most expensive markets of any top Senate race states this cycle. And given the competitiveness of Hagan’s re-election bid, the early spending figures reflect that.

According to media buying figures obtained by CQ Roll Call, Republican outside groups have outspent their Democratic counterparts in North Carolina, $5.7 million to $2.6 million. That includes the $750,000 airtime purchase in early December by Senate Majority PAC and about a $4 million total investment from Americans for Prosperity.

The numbers are based on information provided by media consultants in both parties as of Dec. 10. Not all of the money was spent as independent expenditures, which must be filed to the Federal Election Commission, so exact figures were not available.

Compared with North Carolina, the spending discrepancy between the two parties is closer in other states. Democrats hope to keep pace with the GOP outside groups targeting their incumbents, as well as define Republican challengers before they can define themselves.

Senate Majority PAC Campaign Director Ty Matsdorf said the group is attempting to highlight GOP challengers — specifically North Carolina state Speaker Thom Tillis and Reps. Bill Cassidy of Louisiana and Tom Cotton of Arkansas — who advocate “irresponsible and dangerous policies.”

“Since some of these candidates aren’t that well known, it is important that voters know where they stand on these issues, so they can’t hide from their records,” Matsdorf said.

In Kentucky, where McConnell is the top target of national Democrats, GOP-aligned groups have spent $2.3 million to $1.2 million from Democrats. That doesn’t include the $700,000 spent by Senate Conservatives Fund, which is backing McConnell’s primary opponent, businessman Matt Bevin.

Senate Majority PAC launched on Dec. 13 a quarter-million-dollar buy in support of Landrieu in the Bayou State. Before that, Republicans had outpaced Democrats in the state by about $1.75 million to $320,000.

As Landrieu distanced herself from the president on Obamacare in her latest spot, the super PAC ad directly targeted Cassidy, Landrieu’s top opponent, on Medicare and the government shutdown. The group’s recent ad in North Carolina defended Hagan on health care and took aim at Tillis.

In Arkansas, Pryor has seen about $1.8 million spent against him, though a sizable chunk of that came from the Michael Blooomberg-founded group Mayors Against Illegal Guns. Democrat-aligned groups have spent about $450,000.

A fifth state likely to see TV ads for the next year is Alaska. A super PAC set up to defend Democratic Sen. Mark Begich has already placed a $100,000 ad buy to defend the incumbent from outside group attacks.

Its ad mocked an Americans for Prosperity spot that had slammed Begich on the issue of Obamacare, noting that the woman featured in it was an actress from the East Coast.

“Honestly we weren’t planning to come out this early,” Jim Lottsfeldt, treasurer of the pro-Begich super PAC, told Alaska Public Radio Network. “But it’s clear in 2014 politics across the nation, the Koch brothers are on the attack and we thought it was smart to start our defense sooner rather than later.”

Outside groups aren’t the only ones on the air, as Pryor, Landrieu and McConnell have all aired their own TV ads. McConnell’s first spot came in mid-March, and he’s topped $1 million in media spending already.

Pryor, widely considered the most vulnerable Democrat up this cycle, has spent well more than $800,000 on ads, including his most recent spot that highlighted the importance of the Bible in his life. That’s at least $500,000 more than Cotton, who recently featured his mother in an ad.

That’s one reason Sen. Marco Rubio’s, R-Fla., leadership PAC ran its own independent expenditure TV ad this month in support of Cotton.

“Normally we wouldn’t go in this early,” said Terry Sullivan, director of Rubio’s Reclaim America PAC. “But he’s getting outspent dramatically, so we wanted to come in and help him.”

There has been outside spending in several other states, including West Virginia and Montana — two of Democrats’ most vulnerable open seats. As the landscape inevitably shifts over the next six months, spending will undoubtedly pick up in other states as well.