The relationship has thawed, but with four more years ahead for Lula, several issues could reignite tensions.
Brazil accused the US earlier this year of trying to cast doubt on its electoral system and denied visas to two state department officials planning to visit.
The US called this “baseless” and revoked the Brazilian ambassador’s visa in response.
If Trump keeps calling this result “rigged”, further diplomatic fallout is likely.
Lula has also vehemently opposed US military action in the region, from the seizure of Nicolás Maduro in Venezuela to the bombing of alleged drug-trafficking vessels.
He lambasted Washington for designating Brazil’s two major gangs as terrorist organisations after lobbying from Flávio Bolsonaro, and warned of attacks on Brazilian sovereignty.
It is a sensitive subject for a political left that remembers the region’s brutal 20th Century dictatorships, many backed by the CIA in the name of stopping communism.
Then there is US tech.
Lula’s campaign accused Meta of favouring Flávio Bolsonaro.
Meta denied this but admitted moderation issues and technical errors had wrongly removed some posts or limited their reach.
Lula’s supporters responded by sharing his messages through a 10-million-strong WhatsApp group to bypass the algorithms.
Separately, the Trump administration is unhappy with Pix, Brazil’s instant payment system, which has boosted the economy, but which the US sees as taking business from Visa and Mastercard.
The relationship has exposed political divisions.
In the campaign, Bolsonaro supporters waved US flags at their rallies and, in one case, an inflatable saying “Trump Nuke Brazil”, while Lula and his supporters accused Flávio Bolsonaro of protecting US interests over Brazil’s.
Still, tensions can be overstated.
The US remains Brazil’s second-biggest trading partner after China, and for now the two leaders get on.
Whether that lasts will depend on how far the US tries to intervene in Brazilian affairs, and how bullish Lula is in response.