Former Florida Governor Jeb Bush speaks at the Detroit Economic Club February 4, 2015 in Detroit, Michigan.National Journal

The GOP could have a dozen deep-pocketed presidential contenders, and they'll all learn next year that when it comes to actual votes, that extra money doesn't buy what it used to.

Already, super PACs are arming second- and third-tier candidates with tens of millions of dollars while the supposed GOP front-runner, Jeb Bush, promises a record-setting haul. This combined fundraising guarantees that by the time Republicans have picked their nominee in summer 2016, the candidates will have spent more to reach voters than ever before.

But to what end? At some point "“ after the candidates make an initial investment of tens of millions of dollars for voter outreach in paid media and the ground game "“ the money available to spend simply can't buy the advantage it once did. And that's because the primary contest will still depend mightily on the outcomes of each of the first four contests, all of which provide invaluable momentum and none of which are held in large or expensive states where candidates have to invest heavily to have an impact.

We're talking about races in Iowa, New Hampshire, South Carolina, and Nevada, where candidates are competing for mere thousands of voters who will be inexpensively inundated with TV ads, political mailers, and front-door conversations with paid staffers. In these decisive contests, the difference between spending $10 million and $15 million yields a minuscule advantage, if any at all.

"You have this tidal wave of money pouring through into these very small spigots," said Elizabeth Wilner, senior vice president of Kantar Media Ad Intelligence, which tracks campaign spending on TV. "Your sights are just set ever more narrowly, and yet you have this immense amount of money to use and try to reach these people. Eventually, you do hit that end to a return on your investment and it does become waste."

Certainly, money will still be essential in 2016, and it remains an advantage to have more of it than anyone else. In an extended primary, when the race moves on to larger states for votes held on the same day, an outsized bank account could yet play an important role.

But diminishing returns on cash investments undoubtedly shift the burden of securing the win back on to the candidate and his or her skills: These contenders will need to demonstrate an ability to click, in real time, with voters and offer a compelling message rather than simply relying on slick strategy to sell them digitally. In effect, the Republican presidential primary could become like the general election for the presidency, where the massive amounts of money spent by each party cancels itself out and rarely leads to substantial returns with voters.

That's bad news for the candidates who are struggling to connect—namely Jeb Bush, whose current front-runner status hinges mostly on the expectation that he will outraise, not outperform, his rivals.

His wallet won't help him in Iowa, where the amount of money spent per voter could reach astonishing heights, driven not only by Bush but the five other Republicans who actually stand a chance of winning the state. Typically, the winner of the caucuses—Rick Santorum in 2012—receives about 30,000 votes. Winning candidates who spend $10 million, then, would spend about $330 per vote. At $30 million—the amount raised by Ted Cruz's flotilla of super PACs after he declared he was running for president—it would mean a whopping $1,000 was spent per vote.

"It's hard to imagine what all they would spend it on at a $30 million mark," said John Stineman, a Republican strategist based in Iowa. "You could. There are always ways to spend it. The question is, how much more are you getting from it?"

It's not even clear how much money can realistically be spent on TV ads in the state. A Des Moines Register analysis found that in last year's Senate race, both sides spent about $41.2 million during the general election. Republican strategists in the state say it's difficult to imagine how more money than that could be spent on TV ads in the primary, given that the airwaves were full during the Senate race.

New Hampshire, which is smaller than Iowa, isn't much more expensive despite the presence of the expensive Boston media market. The winner of Nevada's primary in 2012, Mitt Romney, won just 16,000 votes. (The state is trying to broaden the number of voters who participate by switching to a primary.) And though South Carolina is much larger than the other early states and will likely have far more than a half-million voters during its primary next year, candidates will struggle to spend more than $5 million there, according to state party Chairman Matt Moore.

"There's a necessity to spend money, but at some point, there are diminishing returns," Moore said.

For sure, the advent of super PACs has given rise to the possibility that the early nominating contests are no longer determinative because flush candidates can afford to hold onto hope longer than ever before.

And for those candidates, the working hypothesis is that when the primary reaches mega-states such as Florida, the difference between a campaign capable of spending $30 million and one spending $15 million becomes stark. Indeed, the later states were important last time, when in the final competitive contests of the primary, Romney was able to significantly outspend Santorum in Michigan and Ohio, an edge that helped him stage a handful of come-from-behind victories that eventually led him to lock up the nomination.

But it's important to remember that Romney had already won one of the first three—New Hampshire. In fact, no Republican candidate in modern history has won the GOP's presidential nomination without winning either Iowa or New Hampshire, and until Newt Gingrich's victory in South Carolina in 2012, the eventual nominee had always won there, too.

Bush likely will have to win one of those states. And if he uses his financial advantage smartly in the early states where he's a long shot to win, he could outspend not for his own direct benefit but to hurt his most direct competition—Scott Walker and Marco Rubio.

"You will have the advantage of playing the three-dimension chess and others will be stuck with the 2-D board," Stineman said.

Still, if the early fundraising returns are any indication, any candidate who lasts months into the primaries will have much more money than Santorum did in 2012. And even candidates who depended on super PAC money later in the campaign—Santorum and Gingrich—each won an early nominating contest.

The momentum earned from those victories can carry a lot of weight with voters in later primaries. And it'll take more than a lot of money to do so.

"Is there some cap on how much you can spend on Iowa or New Hampshire before you start seeing almost no return?" Wilner asked. "I think this might the cycle when we figure out where that cap is."

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