The United States invasion of Mexico in 1846 inflicted a painful wound that, in the 170 years that followed, turned into a scar. Donald Trump has torn it open again.

Among the many lies that he has constructed, none is more ridiculous than his attempt to contradict history by presenting the United States as a victim of Mexico, a country that supposedly steals jobs, imposes onerous treaties and sends its “bad hombres” across the border.

To confront this fake history, some Mexicans are proposing to remind Mr. Trump exactly what country was the first victim of American imperialism. They are calling for a lawsuit that would aim to nullify the Treaty of Guadalupe Hidalgo (signed on Feb. 2, 1848), in which Mexico — invaded by American soldiers, its capital occupied, its ports and customs stations seized — was forced to accept the American annexation of Texas and concede more than half the rest of Mexican territory, now including most of the states of Arizona, New Mexico and California.

This effort is being led by Cuauhtémoc Cárdenas, the elder statesman of the Mexican left. Mr. Cárdenas is convinced that the Mexican government — especially given the need to confront Mr. Trump’s aggression — has a solid legal case.