Randy Feenstra

Zach Lahn defeated Rep. Randy Feenstra by less than a percentage point in the Republican primary for governor of Iowa.

While Feenstra outperformed Lahn in Iowa's 4th Congressional District, where he is currently serving as U.S. Representative, he underperformed in other districts.

When Iowa Gov. Kim Reynolds announced she wouldn't seek reelection, it created this year's wide-open Republican primary to replace her at the top of the party’s ticket for the 2026 midterm elections.

But Tuesday's Election Day ended up being even more wide open than most expected, with political upstart Zach Lahn upsetting the favored Rep. Randy Feenstra in a five-man race to capture the Republican nomination for governor.

As the dust settles from a dramatic final week that included President Donald Trump's late endorsement of Feenstra, the question has shifted from “could Zach Lahn win?” to “how did Zach Lahn win?”

We dug into the election data to find out. Here's what it says about Lahn's upset win.

Zach Lahn established solid voting base throughout Iowa

Spend enough time watching Iowa politics, and you’ll see familiar patterns emerge on the state’s 99-county chessboard: More heavily populated, liberal strongholds around Des Moines and Iowa City; a union-driven eastern Iowa voting bloc; and ruby-red swaths of conservatives in the north, west and south.

But the county-by-county voting results map for the June 2 Republican governor primary seems … unusual this time around.

Part of that is the nature of a five-person primary: In addition to Lahn and Feenstra, former state administrator Adam Steen and former state Rep. Brad Sherman made it onto the map by each winning at least one county.

Beyond that, the familiar geographical lines of political analysis don’t fit as well for this primary.

Yes, Feenstra won every county on the Mississippi River, and Lahn controlled central Iowa. But look at the four northwesternmost counties in Iowa: Often among the most conservative in the state, they split their vote — two counties went to Lahn, two went to Feenstra, and none had less than a 5-point vote margin.

Johnson and Linn counties in eastern Iowa, which also tend to both vote more liberal, also split between the two frontrunners.

So, let’s zoom out and look at the results by Congressional district.

Feenstra represents Iowa’s 4th Congressional District, so you would expect him to win that district in the western half of Iowa. And he did — but not by much.

Feenstra had a roughly 4-point advantage over Lahn in the 4th District, which contains the most Republican voters. The 2nd District in northwest was more or less a dead heat, and Lahn had a slight advantage in the 1st District.

But where Lahn had the greatest success — and Feenstra the least — was the 3rd District, which contains southern and central Iowa, including Des Moines. Lahn had a nearly 7-point victory margin over Feenstra in that district.

Lahn’s support was nearly identical in each congressional district: around 37% or 38%.

Feenstra’s support was more volatile, swinging nearly 10 points between the 3rd District (his worst) and the 4th (his best).

Zach Lahn stays above 35% vote threshold to win outright

Lahn needed that consistent support across Iowa, because as election night wore on, he was essentially running two races: One against Feenstra, his primary opposition, the other against the possibility of the race going to a convention.

In Iowa, a primary winner must take at least 35% of the vote to earn their party’s nomination. If no candidate reaches that threshold, then the nominee is determined at a party convention.

Lahn avoided that. His vote share remained a few percentage points over the threshold all evening, and in the end, it was Feenstra, not a potential convention, that was his closest opponent.

Lahn’s support also remained consistent from county to county. He earned at least 30% of the vote in 88 of Iowa’s 99 counties and reached 35% in about two-thirds.

While Feenstra posted similar totals, Lahn saw higher levels of support in more counties: He earned 40% of the vote in 40 counties to 32 for Feenstra.

That consistent support across the state helped insulate Lahn against the sort of variance that can occur in a five-person race.

Pipeline concerns didn't play a major role in deciding the race

Among the key issues in the Republican primary was the potential use of eminent domain to acquire land to build carbon-capture pipelines, particularly in northwest Iowa.

While Feenstra has said he opposes such uses of eminent domain, other candidates in the primary took stronger stances in opposition as part of their campaigns.

But the primary results suggested that, at least on a surface level, the pipeline issue didn’t cost Feenstra.

In the counties through which proposed pipelines would extend, Feenstra had a 6-point advantage over Lahn. In unaffected counties, Lahn had a 3-point advantage.

There’s significant overlap between the 4th Congressional District and the counties that would be affected by the proposed pipelines, but Feenstra performed even better in pipeline counties than he did in the 4th District as a whole.

Did other Republican governor candidates play spoiler?

In any race with more than two candidates, it’s easy for supporters of a losing contender to blame ancillary candidates for siphoning away votes.

That’s even easier when there’s five candidates. But the muddled field also makes it hard to definitively say whether any one candidate prevented any other from winning.

One way of measuring the issue is to compare how the two leading candidates performed head-to-head against each other candidate across all 99 counties.

In most cases, you would expect to see candidate A’s total increase as candidate B’s total decreases, and vice versa. But not every pairing shows quite so direct a correlation.

Fifth-place governor candidate Eddie Andrews, for example, shows little or no correlation with Lahn or Feenstra. The percentage of votes Andrews received appeared to have no impact on the percentage of votes Lahn or Feenstra gathered.

The correlation between Lahn’s and Feenstra’s results are much stronger: In counties where Lahn received more votes, Feenstra tended to receive fewer.

But two even stronger correlations appeared between Feenstra/Steen and Lahn/Sherman. In any given county, Steen earning more votes correlates with Feenstra receiving fewer votes — even more so than compared with Lahn.

While Sherman’s results show almost no correlation to Feenstra’s totals, Sherman's correlation to Lahn’s results is stronger than between the two frontrunners.

That’s a lot of dataspeak, and it’s worth noting that none of these relationships can be considered overwhelmingly strong. Therefore, in a five-person race, it's virtually impossible to say how the outcome would have changed if different candidates were or weren’t involved.

But elections with such thin margins tend to produce a lot of what-ifs, and this is one of the more interesting ones unsuccessful candidates may well be pondering as they look back on Election Day.