Stephen R. Kelly, a former U.S. diplomat who served in Mexico from 2004 to 2006, teaches at the Sanford School of Public Policy at Duke University.

In a scene that would have given Donald Trump heart palpitations, 200 flag-waving Mexican troops breached the U.S. border outside Laredo, Tex., 10 years ago and advanced unopposed up Interstate 35 to San Antonio.

It was the first time a Mexican army had marched on San Antonio since 1836 when Gen. Santa Ana massacred besieged Texas independence fighters at the Alamo.

This time, however, the Mexican soldiers were on a relief mission to feed tens of thousands of homeless and hungry Americans displaced by Hurricane Katrina. Setting up camp at a former Air Force base outside San Antonio, they distributed potable water, medical supplies and 7,000 hot meals a day for the next three weeks.

If this doesn’t sound like the Mexico you’ve been hearing about lately — the one that has been ripping America off, the one that sends rapists and criminals across the border — you might want to consider this little-known gesture of humanity from our abused southern neighbor as you think about Katrina 10 years later.

I was serving as the No. 2 at the U.S. Embassy in Mexico City in August 2005 when Katrina made landfall on the Gulf Coast. The storm’s track posed no danger to Mexico, and we followed events like most expatriate Americans — aghast, but at a distance.

But not Mexicans. They were watching the same scenes of floating corpses and botched relief efforts in New Orleans. My chief contact at Mexico’sForeign Ministry called to say the Mexican army had two field kitchens that could feed storm victims who had made their way to Texas, he said, and the navy had two ships that could help with cleanup efforts in New Orleans.

I told my contact the offer was very generous, noted that many countries had offered assistance, and added that the State Department and the Federal Emergency Management Agency would decide which offers to accept. He said it was too late for that. The convoy had already left Mexico City on its way to the border, and the ships were ready to steam from Veracruz.

To put this in context, the United States likes to think of itself as the country that does the helping, as we had done when Mexico City was struck by a devastating earthquake in 1985. But few had contemplated the possibility that Mexico would be coming to help us.

The next 48 hours were a mad scramble to get Washington to say yes, to figure out how to admit more than 200 military personal without passports or visas, and to recognize that the Mexican army, traditionally one of the most nationalistic and anti-American elements in the Mexican government, was making an extraordinary gesture.

It worked. The 45-vehicle convoy crossed the border at Laredo at dawn on Sept. 8 and arrived in San Antonio later that day. The only glitch was that the USDA would not allow the Mexicans to serve the beef they had brought because they couldn’t prove it had been produced in a mad-cow-free facility. Undeterred — and un-insulted — the Mexicans bought their beef locally.

By the time their mission in San Antonio ended Sept. 25, the Mexicans had served 170,000 meals, helped distribute more than 184,000 tons of supplies and conducted more than 500 medical consultations.

Mexican sailors also assisted with clearing downed branches and other storm debris in Biloxi, Miss., where they posed for photos with President George W. Bush, who thanked them for their help.

Nobody was more surprised by this humanitarian mission than the Mexican military itself. Perhaps pumped up by its unexpected display of competence and compassion, even for a normally haughty northern neighbor, the Mexican army became far less defensive , and more willing to cooperate with its U.S. counterpart.

Disasters such as Hurricane Katrina, or the spectacle of U.S. presidential politics, often force to the surface the true character of the players. The Mexicans proved they were neighbors we can count on. One can only speculate how Trump would have handled the Mexican invasion had he been president. Would he have considered the visa-free Mexican soldiers illegal immigrants? Would he dispatch rape kits to San Antonio-area hospitals?

We should try to answer those questions soon. Because hurricane season is again upon us. And you never know when you are going to need a friendly neighbor, and a hot meal.