It’s only one warning sign, but a serious one: In Saturday’s special election in a Texas state Senate district that President Donald Trump carried by 17 points just 14 months ago, a Democrat just spanked a Trump-endorsed Republican by 14 points.

That 31-point swing in a ruby red district outside Fort Worth has more than one cause, but it’s still a clear sign of swing-voter discontent.

For all the wins Trump is racking up in foreign policy, and early signs of a fast-improving economy, the scenes of Border Patrol and ICE agents shooting civilians — capping other hyper-aggressive Homeland Security actions in Minneapolis — revolt the moderate voters Republicans need.

Sending border czar Tom Homan to do the job right was a good move, but the public now needs to see a prolonged period of rational enforcement — or, better still, not see much enforcement because it’s being done with due regard for law and order.

Let the wild protesters make the negative headlines, while the prez and his people make positive ones.

Americans want the border secured and dangerous illegal aliens out of the country; they don’t want federal agents dragging people out of cars and barging into private homes in search of people who might merit arrest.

Dems carried that Texas special with extraordinary Democratic turnout and a tepid Republican showing; one side had reason to express its fury, the other no cause to show enthusiasm.

If Team Trump can’t fully turn the page on Minneapolis — and the left will strive to prevent it — America will be looking at Speaker Hakeem Jeffries in January, and maybe Senate Majority Leader Chuck Schumer too.