This year’s presidential primaries have already broken several rules of politics, and new spending data suggests another shift in modern campaigning – a decline in polling, at least among GOP candidates.

In the three months leading up to the Iowa caucus, many Republicans spent little to nothing on polling. Marco Rubio and Jeb Bush each spent just over $150,000 on campaign polls, while the two non-politicians in the race, Ben Carson and Donald Trump, declined to buy any polling research at all. The data is from the campaigns’ spending summaries for the final quarter of 2015, which are released under federal election law.

Ted Cruz was the only Republican who spent much on polls – over $380,000 – and his campaign threw another $3 million into separate data for “donor modeling.” In Iowa, Cruz’s campaign proved adept at using field and targeting data, not simply public opinion polling, to locate and mobilize his supporters.

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“For winning a tactical battle in these early primary states, polling is a lot less useful and seems to fade in accuracy in every cycle,” said Michael Simon, analytics director for the Obama 2008 Campaign.

Donald Trump led many public polls in the primary pre-season, but those surveys proved wrong in Iowa and may have even led his strategy astray. Media polls focus on the broad horse race, especially the frequent “national” polls of the entire electorate, which have less relevance to a race decided by a smaller number of state electorates. Effective campaign polling and data, by contrast, can inform a campaign’s strategy of whom to target and where to spend resources.

For candidates like Kasich and Christie, foregoing polls may have been a budgetary necessity. For Trump, it may have been a costly miscalculation.

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“Trump doesn’t understand it – as he was quoted the other day: ‘Why would you pay for polling when the networks are doing it for you?’” explained a Republican strategist familiar with Trump’s thinking and not supporting any of his rivals.

“He doesn’t understand it as a predictive or testing tool,” the strategist told NBC. “He’s only interested in ‘Am I ahead or behind’ – which is the least important thing if you’re using polling for predictive purposes.”

Without a pollster, the strategist noted, the Trump campaign cannot test whether it is more effective to attack Ted Cruz for his past support for Chief Justice John Roberts, for example, or on questions about his Canadian citizenship. That doesn’t mean Trump’s gut is always wrong, the source added. “He decided that Jeb was ‘low energy’ – how’d that work out?” the strategist asked. “Jeb’s dead.”

On the Democratic side, however, polling is alive and well this cycle.

Hillary Clinton spent $720,000 on polls last quarter – as much as the six top Republican candidates combined. About $477,000 of that went to the firm of Joel Benenson, a pollster for Mrs. Clinton, Bill Clinton and Barack Obama. In the previous quarter, Clinton’s polling bill was even higher – at $1.9 million.

Simon, the Obama campaign veteran, said the tab must reflect planning for a national race.

“There’s no way to spend $700,000 in three states on polling,” he told NBC. “It’s got to be a larger set of polling, or something else there.”

This is like buying world’s most expensive yacht for Transatlantic race & not buying GPS or charts. https://t.co/6Ou7V3J7qd — stuart stevens (@stuartpstevens) February 5, 2016

While Bernie Sanders has campaigned as an outsider who will change conventional politics, as his fundraising has excelled, his campaign has begun spending handsomely on polls. In the third quarter last year, he spent $52,000 on research, listing no outlay on polls. In the most recent quarter, his polling bill jumped above $500,000 – more than any other Republican candidate.