BUENOS AIRES, Argentina >> When Barack Obama’s state visit to Buenos Aires was announced early this year, Argentina’s new president cast it as a sign that the South American nation was on a U.S.-backed path to investment and modernization that would help it conquer its economic problems.

But in the weeks leading up to the U.S. leader’s arrival early Wednesday, Argentina’s attention hasn’t been on the future, but rather on painful chapters in its past — and unanswered questions about the United States’ relationship with one of the most repressive military dictatorships in Latin American history.

The catalyst has largely been the timing: Thursday marks the 40th anniversary of the military coup.

“The dictatorship is still very much on the table” in Argentine society, said Roberto Bacman, director of the Center for Public Opinion Studies, a South American research firm. “This visit is going to bring out some dark sides of the past.”

Some groups have promised protests in Buenos Aires and Bariloche, a tourist city in southern Argentina where Obama will spend part of Thursday. They argue that during the Cold War, the United States backed dictatorships, including Argentina’s, and so the presence of an American leader is disrespectful to families of the thousands who died or were disappeared.

Even without the visit, memories of military rule between 1976 and 1983 haunt the country, affecting political ideology and feeding debates about whether the country should continue to spend millions of dollars every year prosecuting former dirty war perpetrators and searching for the remains of the missing.

Human rights groups estimate about 30,000 were killed or disappeared, though official estimates are around 13,000.

The trip to Argentina followed Obama’s historic visit to Cuba, where the two nations agreed to accelerate the thawing relations after more than 50 years of animosity. Obama will also arrive just a day after terror attacks in Brussels killed at least 31 people.

As the controversy grew last week, the Obama administration surprised many across the country of 41 million people by announcing plans to declassify CIA, FBI and other secret documents related to the dictatorship. Human rights groups have been pushing for years for such a document dump.

In 2002, the U.S. released more than 4,000 State Department documents from that period, but they raised more questions than answers. For example, notes from a 1976 meeting between Secretary of State Henry Kissinger and Argentina’s foreign minister seemed to show Kissinger green-lighting a clampdown on dissidents.

“If there are things that have to be done, you should do them quickly,” Kissinger said, according to a transcript.

Carlos Osorio, director of the Southern Cone documentation project for the non-governmental National Security Archive in Washington, said other documents will surely have much more information about what U.S. officials knew, when they knew it and whether they aided the repression.

“It’s important for Argentines, and relatives of victims will be relentless” in trying to get information, said Osorio. “It’s important for the United States to extend its hand and recognize what we did.”

A day before Obama’s announcement, during an interview with The Associated Press, Argentine President Mauricio Macri sidestepped questions about whether he would bring up the past with his U.S. counterpart. Instead, Macri focused on his hope for a strong relationship with the United States moving forward.

Still, minutes after the announcement, Macri’s chief of staff Marcos Pena hailed it as “transcendental.”

“We believe it’s a huge gesture,” Pena told a local television station.

Macri, who campaigned on promises to overhaul the economy, would clearly rather spend his time courting the international investors expected to come for Obama’s visit. But embracing a close examination of the past could help him politically.

Macri won last year’s runoff election by only 2.5 percent of the vote. As the son of one of Argentina’s richest men, he has long been accused by left-leaning human rights groups of being impervious to the struggles of the poor and disinterested in uncovering the abuses of past right-wing rulers.

Human rights groups haven’t gone so far as to say Obama is now welcome. But they have celebrated the decision to declassify the documents.

“This is a grand gesture on the eve of (Obama’s) visit to our country,” the iconic Grandmothers of the Plaza de Mayo human rights group said in a statement. “The United States has shown its willingness to respond to the families and victims of crimes committed by the dictatorship.”