WENDELL, N.C. — Very few things will stop an Americans for Prosperity field associate from knocking on your door.

A dog on the porch is one of them.

“We don’t test that,” Donald Bryson, AFP’s North Carolina state director, said last week on a Thursday morning canvassing effort to convince voters in the state’s 2nd Congressional District to oppose Rep. Renee Ellmers (R-N.C.) in Tuesday’s House primary.

Bryson spots the dog from the driveway and promptly turns around. He marks the house “restricted access” on his iPad — using an app created specifically for these grassroots door-to-door efforts — and moves on to the next target.

At the vast majority of houses that Bryson and 16 other AFP staffers will knock on during a recent morning, residents are either not home, don’t answer the door, or decline to discuss politics. Each house gets marked with its own color-coded designation on the app: red if the property was restricted or had a

“No trespassing” sign, for example; blue if no one answers the door; green if AFP has spoken to the resident directly; black for houses that have yet to be tried.

It’s all part of the Koch-backed group’s aggressive effort to topple Ellmers, who they think is too cozy with the Washington establishment and has backed such objectionable things, in their book, as renewing the Export-Import bank. This is the first time that AFP has intervened in a congressional race against a Republican and they’re spending on television and digital ads, as well as knocking on 12,000 doors in suburban and rural Raleigh.

A reporter accompanied them as they did so in a peek at how the powerful group’s tactics work on the ground.

Wendell, a town about 25 miles east of Raleigh, was originally part of the 13th district that used to be represented by Ellmers’s toughest primary foe and the man observers say has the edge on Tuesday, Rep. George Holding (R-N.C.). Holding and Ellmers were thrown into the same 2nd district after a panel of federal judges ruled in February that two of North Carolina’s House districts were drawn in such a way as to disadvantage African-American voters,

AFP zeroes in on residents based on their voting record, which indicates their likelihood of voting again in a primary, and examines consumer data, such as where they shop and what they buy.

Typically, one out of every five houses results in a real conversation. Residents in rural areas tend to be chattier than those in suburban neighborhoods, Bryson said. Wendell, where tobacco fields line the roads and chickens roam freely in front yards, is considered somewhere in the middle — suburban transitioning into rural.

“In the rural areas, people tend to be much more conversational,” Bryson said. “People don’t come knocking on their doors out here.”

The longest such conversation Bryson recalls was in 2012, when a man chatted him up for 30 minutes on his lawn chair, even bringing out lemonade.

AFP associates are trained to follow a script, which starts out by asking if they “Are you aware there’s a special primary election on June 7?” and “Do you know who you’re going to vote for?” The statements eventually becoming more pointed: “We’re asking you to vote against Renee Ellmers.”

Of the handful of residents who did answer their doors that morning, few needed convincing to vote against Ellmers.

Bucky Hinnant, 70, said he plans to vote for Holding next week. He is particularly troubled by Ellmers’ vote for the 2016 budget, which he is concerned will worsen the national debt.

“The one thing that teed me off was when she voted for that budget,” said Hinnant, a retired engineer. “That P.O.-ed a lot of people here like myself. It was too much money. There comes a time you need to draw a line in the sand.”