Will all the midterm ad spending matter?

If you live in a battleground state, you can't escape the television ads. And the mail. And the phone calls.

Which means you're not imagining the fact that candidates, political parties and interest groups are spending a record amount of money for next Tuesday's midterm elections. The question is what difference that money makes in the outcome.

Consider the extent to which raising and spending money has gone up. In 2006, when Democrats pushed to recapture control of the House and Senate, it was a $2.8 billion midterm election. Four years later, when the tea party fueled a Republican resurgence in the House, $3.6 billion.

The 2014 ledger remains incomplete, of course, but the Center for Responsive Politics has projected a total of $4 billion this year. And that doesn't count some of what it calls "dark money" that isn't reported to the Federal Election Commission.

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Much of that money circulates outside the campaigns on individual candidates. Business groups like the U.S. Chamber of Commerce counter spending by organized labor; environmental groups square off against the energy industry. That outside spending has swelled for years, even before the 2010 Citizens United decision from the Supreme Court. Outside spending will end up around $900 million this cycle, more than triple the 2006 total.

The money from sectors of the economy flows in waves that vary with political conditions. Just over half of Wall Street's money favored Republicans in 2006, amid rising discontent with President George W. Bush and the Iraq War. This year, with President Barack Obama losing altitude, Wall Street money is 62 percent Republican.

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Chris Maddalon | CQ Roll Call | Getty Images

High-tech money favors Democrats—55 percent in 2006, up to 60 percent this year. Energy money has gone in the opposite direction as Obama has pressed his agenda on carbon emissions and climate change; it's 78 percent Republican this year, up slightly from 74 percent in 2006.

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Two principal factors shape the overall totals: who holds power (incumbent parties in the White House and Congress command more) and who has political momentum. In 2006, Republicans controlled all of Washington, which helped them to an $84 million Team Red spending edge over minority Team Blue. In 2010, Democrats held control but Republicans had momentum, which resulted in a slim $40 million Democratic edge.

This year power in Washington is split but momentum favors Republicans. That translates into a projected $157 million edge for the GOP.

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That sounds like a lot until you realize that it's just 4 percent of overall spending, and that candidates in all tightly contested races have more than enough money to get their messages out. Spending in battleground campaigns usually passes the point of diminishing returns.

That's another way of saying that many factors—geography, demography, political mechanics, national mood—can decide the 2014 battle for Congress. But campaign money isn't likely to.