Federal elections are enormous money pits, with campaigns and outside groups spending millions of dollars to influence the outcome.

This year will be no exception. In fact, it could obliterate the record for midterm election spending, with looser finance rules, close contests, and a Tea Party insurrection all driving up the total amount of money spent on winning congressional seats.

Spending by outside groups in particular is on pace to reach an unprecedented level this cycle. To this point in 2010, outside groups had spent $10.4 million in what would become, by a wide margin, the most expensive midterms ever. To date, such groups have spent more than three times as much, $36.7 million, on the 2014 races.

Case in point: Americans for Prosperity, founded by the conservative billionaire Koch brothers, has already spent $8.2 million on ads in North Carolina, according to Politico. AFP has spent $12 million total on the six tightest Senate races combined, and more than $27 million since August attacking Democrats in the Senate and House over ObamaCare. At this rate, AFP will easily outstrip the $38.5 million it spent on the 2010 midterms.

Much of the money boom can be traced back to the Supreme Court's January 2010 ruling in Citizens United v. Federal Election Commission, which allowed corporations, labor unions, and other groups to spend unlimited sums for or against candidates. Combined with a few other lower court rulings, the decision opened the floodgates for outside spending.

Returning to the above chart, you can see where outside spending was flat for years (in non-presidential races) before blowing up in 2010.

"We knew this election could make spending history," Sheila Krumholz, executive director of the Center for Responsive Politics, said in 2010, "but the rate of growth is stunning."

Some of that spending spike came from the rise of massive super PACs. But Citizens United also boosted 501(c)(4) organizations, which spend as lavishly as super PACs, but are tax exempt and don't need to disclose their donors.

Now, the free-for-all nature of the 2014 election cycle is only further fueling an influx of outside money.

Republicans have a very good chance of flipping the Senate. Democrats have more seats to defend, some of which are in toss-up states. And the sluggish economy, Obama's middling popularity, and public dissatisfaction with ObamaCare could all work against Democratic incumbents. North Carolina Democratic Sen. Kay Hagan is a prime example of that predicament, hence AFP's media blitz in the state.

But the GOP's desired Senate takeover could be upended by, well, Republicans themselves. The party is caught up in a nasty civil war, with outside conservative groups vowing to defeat incumbent Republicans with primary campaigns. As we've seen in the past with far-right candidates like Todd "legitimate rape" Akin and Christine "I'm not a witch" O'Donnell, these insurgent campaigns often backfire.

Still, the Senate Conservatives Fund, which backed a who's who of lightly credentialed, Tea Party-aligned, losing candidates in the last midterms, has already spent as much money this cycle as it did in all of 2010. On the flip side, the Chamber of Commerce has said it's prepared to spend $50 million against Tea Party challengers.

"Our No. 1 focus is to make sure, when it comes to the Senate, that we have no loser candidates," the Chamber's Scott Reed told The Wall Street Journal. "That will be our mantra: No fools on our ticket."

Add it all up — and factor in the unprecedented cash party committees and campaigns themselves are already hauling in — and 2014 is shaping up to be the most expensive non-presidential election year ever. With a slew of close contests, all those millions of dollars in outside spending could very well make the difference between Democrats holding, or losing, control of the Senate.

Of course, there's still a long way to go till November. But already in this cycle, outside groups have nearly outstripped their total spending in 2006 ($37.4 million). In 2010, outside groups' spending ballooned to $205.5 million, and overall election spending (including that of congressional campaigns and party committees) eclipsed $3.6 billion.

That's a huge number. But if the early expenditures of the current cycle are any indication, 2014 will blow that 2010 record out of the water.