Brazil has long been haunted by the gap between its potential and its ability to deliver. It possesses the sixth-largest territory on earth, vast natural resources and a population of over 200 million. For most of the 20th century, its economy grew faster than virtually any other country’s. And yet Latin America’s largest nation never quite became what its boosters always insisted it would: a global power of shared prosperity. That maddening, persistent distance between promise and reality is what has made nationalism the master language of Brazilian politics. Whoever could answer the question of why Brazil had fallen short, and what to do about it, held the key to political success.

From the 1920s onward, two broad visions competed for that key. The progressive version held that Brazil’s failure to realize its potential was rooted in inequality and the capture of the state by elites who benefited from foreign exploitation. A broad reformist agenda became the precondition for national development. Under President João Goulart in the early 1960s, this vision took the form of the “reformas de base,” a suite of policies including agrarian reform, voting rights for illiterate Brazilians, limits on profit remittances by foreign corporations and greater state control over natural resources. Against the backdrop of the Cold War, the language of national self-determination became a common idiom of Brazilian democratic politics.

A U.S.-backed military coup in 1964 put an end to that. Instead, the generals who seized power fused patriotic propaganda with violent authoritarianism. In making the case for military rule, Roberto Campos, the regime’s cerebral planning minister, attacked what he called “temperamental nationalism” — which he dismissed as emotional, erratic and economically ruinous — and insisted that market discipline and alignment with Washington constituted the true national interest. The dictatorship’s patriotism, which reached its apogee in 1970 when Brazil won its third soccer World Cup, expected citizens to feel proud of their country without raising uncomfortable questions about who it was serving. Those who did were painted as obstacles to the nation’s development, or made to suffer much worse fates.

The dictatorship ended in 1985, but the battle for the nationalist mantle went on. When Jair Bolsonaro promised during his 2018 campaign that “red criminals will be banished from our homeland” and asserted that “we are the real Brazil,” set to “build a new nation,” he was not borrowing from Mr. Trump’s playbook so much as reaching into his own country’s political inheritance. Conservatives had made similar proclamations throughout the Cold War when denouncing progressive nationalists as insidious subversives. Mr. Bolsonaro updated the content, but the form was the same: Claim the nation, delegitimize the left as anti-Brazilian and insist that what is good for the United States is good for Brazil.

His son has sought to pull off the same trick. Flávio Bolsonaro has made security a central line of attack on Mr. Lula, arguing that the president and his party are soft on organized crime. Turning to Washington, Mr. Bolsonaro helped in May to secure the U.S. designation of Brazil’s two largest criminal organizations as terrorist groups. But the approach comes at a political cost. When Mr. Trump applied new tariffs on Brazilian goods last month, Mr. Lula convincingly cast himself as the defender of Brazilian sovereignty against foreign meddling. The same thing happened last year when Mr. Trump launched a trade war against Brazil at the Bolsonaros’ behest.