SAN ANTONIO — GOP Texas Rep. Tony Gonzales is dangerously close to losing his seat to a gun-fanatic YouTuber after the married pol refused to resign when a staffer burned herself to death over their alleged affair.

Gonzales is in the biggest fight of his political career this week, facing an ugly uphill primary battle amid demands he step down, plummeting party support and a congressional ethics probe over his alleged extramarital tryst.

An ex-congressional staffer for Gonzales who now volunteers for challenger Brandon Herrera — “The AKA Guy” with more than 4 million online followers — told The Post on Sunday that voters were “done with Tony” even before the affair allegations surfaced.

“I don’t feel he was doing enough for the border crisis to stop that, the red-flag laws, and then the last straw was him voting for all the LGBT stuff, same-sex marriage,” said the former aide, who worked for Gonzales at an office in a border county from 2021 to 2023.

In addition to border issues, the source was referring to Gonzales backing “red-flag” crackdowns on gun buyers and greenlighting taxpayer-funded Pride events on US military bases.

At an event in Corpus Christi on Friday, Gonzales, a father of six, got booed by some attendees when President Trump briefly recognized him as one of several Republican candidates he endorsed who are seeking re-election.

The Texas Republican defeated Herrera in a primary runoff two years ago by around 400 votes. The incumbent will no face off again with the YouTuber and firearms enthusiast Tuesday as an internal campaign poll found Gonzales trailing by 24 percentage points, The Post first reported.

The survey, commissioned by Herrera’s campaign, showed the Republican challenger is backed by 45% of likely primary voters, while Gonzales registered just 21% support, followed by former Rep. Francisco “Quico” Canseco and construction executive Keith Barton, who are tied at 4% each.

But another 26% of potential GOP primary voters remained undecided for the late February poll, meaning enough 23rd Congressional District Texans could break for Herrera to get him over the 50% threshold and avoid another runoff this cycle.

The largely rural district comprises the border regions of west Texas, running roughly 800 miles from San Antonio to El Paso. All but a handful of counties in it voted heavily for Trump in the 2024 election.

Herrera has claimed that Gonzales’ “lies” about his alleged affair with his married staffer, who had a child, will let Democrats easily “flip a reliable Republican seat blue” if the three-term congressman prevails in the primary.

Republicans currently hold 218 seats to Democrats’ 214 in the House because of vacancies involving resignations and deaths, putting their majority in peril for the 2026 midterm elections.

“What you’ve seen is not all the facts,” Gonzales told CNN reporter Manu Raju on Capitol Hill last Tuesday while evading questions about text messages that show tragic former staffer Regina Santos-Aviles admitted to an “affair” and how Gonzales pressed her for “sexy” images.

More than half a dozen of Gonzales’ House Republican colleagues have called on him to drop out of the race or resign from office over allegations he had an affair with Santos-Aviles, his regional director, in May 2024 — 16 months before she self-immolated in the backyard of her Uvalde home.

The 35-year-old mother of one told first responders before she died Sept. 14 that “she discovered her husband was cheating on her with her best friend, and as a result, she poured gasoline on herself and set herself on fire.”

Her widower, Adrian Aviles, and a former colleague of Santos-Aviles denied the claim when contacted by The Post. Other police records and an autopsy note that Santos-Aviles had been drinking at the time of the tragedy and taking “antidepressants.”

House Speaker Mike Johnson (R-La.) has called the accusations against Gonzales “very serious” and urged him privately last week “to address” the issue “directly and head on with his constituents.”

The Office of Congressional Conduct began probing the purported affair in November but won’t be able to refer findings to the House Ethics Committee for potential punishments until after the primary election.

A rep for Gonzales did not respond to a Post request for comment.