The political team at the Florida Chamber of Commerce has come across a remarkable trend this campaign season: a huge spike in mail voting by people who rarely vote in primary elections.

Almost half of the mail ballots returned so far for Tuesday's primary election have come from Floridians who voted in either one or zero of the past four primary elections. That means a big, decisive chunk of the vote will come from people who have not been polled, and potentially not courted, targeted or accounted for by countless campaigns across the state.

"This is huge," said Marian Johnson, senior vice president of political strategy for the Florida Chamber and one of the foremost experts on Florida campaigns and politics. "I can envision election night when the votes are counted that certain people win that nobody thought had a chance, and that being attributed to this trend."

As of Thursday morning, more than 855,000 primary ballots had been cast by mail. More than a quarter of those votes came from Floridians who had not voted in the last four primaries and another 20 percent from people who voted in just one of the last four primaries.

In other words, these are not "likely voters" surveyed by most pollsters or targeted by sophisticated political campaigns. The trend applies to Democrats and Republicans alike and across the state, said Johnson, who was shocked when she first spotted the trend developing weeks ago.

"The first thing I did was go back to my data people and said, 'Are you sure you ran this right?' "

They had. The data crunchers looked at who requested mail ballots and who is returning them, and categorized each voter by a zero, one, two, three or four — depending on how many of the last four primaries they voted in.

Among the more than 855,000 mail ballots cast so far, more than 215,000 came from voters who had not voted in the last four primaries, and 171,000 came from voters who have voted in each of the last four primaries. Those "new" primary voters included more than 86,000 Democrats, and more than 90,000 Republicans.

"I believe there are going to be more zeros and ones that vote absentee than threes and fours. . . . We're in unprecedented, unchartered territory," said Florida Chamber president and CEO Mark Wilson. "Nobody's been polling these people, nobody's been marketing to these people."

The Republican-leaning chamber started targeting these infrequent primary voters several weeks ago, Wilson said, declining to identify specific races. In some legislative primaries where a few hundred votes are expected to decide the election, these unlikely voters may be decisive.

Pinpointing the reason for the trend is impossible, but local elections supervisors increasingly are promoting and encouraging people to vote by mail. It's more convenient for voters, less expensive to manage than in-person early voting, and the more people who vote before election day, the less likely polling places are to be overwhelmed.

The combination of Floridians automatically receiving mail ballots and the media focusing constant attention on the presidential election seems to be prompting more people to weigh in on the primary elections that usually generate far lower turnout than the general election.

"I think top of the ticket plays a lot in this. The voters don't like either candidate (Hillary Clinton and Donald Trump), but the emotions of frustration and anger are pushing people to do what they've never done before," said Johnson. "I would think these voters definitely are not looking for status quo."

Nor are these new primary voters likely to significantly help the outsider presidential candidate in November. The vast majority of these "new" primary voters are regular general election voters already, Johnson said.

Rich Heffley, a Tallahassee-based Republican consultant, said the trend identified by the chamber definitely could mean pollsters are off base in some races, but well-run campaigns should already be tracking anyone who has received mail ballots regardless of whether that voter has much history in primaries.

"Everybody monitors those absentee ballot requests. I know who made a request, when the ballot was mailed to them, when it was received, and you can monitor how it has aged — how long it has been sitting on their kitchen counter," Heffley noted. "Once there's a live ballot on the street, people know it."

Contact Adam C. Smith at asmith@tampabay.com. Follow @adamsmithtimes.