Olympic bronze medallist fencer Race Imboden knelt during the American national anthem after winning gold in the men’s team foil, with a second protest then staged by hammer thrower Gwen Berry here at the Lima 2019 Pan American Games.
Imboden had already claimed a bronze medal in the individual men’s foil event, before topping the podium in the team competition alongside Gerek Meinhardt and Nick Itkin.
The 26-year-old, the world number two, then knelt as the American national anthem was played during the medal ceremony.
The act is seen as a civil rights protest, started by American football player Colin Kaepernick in 2016.
Kaepernick had knelt to highlight police brutality and racism.
The stance has become more commonly referred to as "taking a knee".
Imboden, a men’s foil team bronze medal from the Rio 2016 Olympic Games and world champion, posted on Twitter to explain his decision to take the knee after the event.
"We must call for change," he said.
"This week I am honored to represent Team USA at the Pan Am Games, taking home gold and bronze.
"My pride however has been cut short by the multiple shortcomings of the country I hold so dear to my heart.
"Racism, gun control, mistreatment of immigrants, and a president who spreads hate are at the top of a long list.
"I chose to sacrifice my moment today at the top of the podium to call attention to issues that I believe need to be addressed.
"I encourage others to please use your platforms for empowerment and change."
The US has suffered from three mass shootings in the past two weeks, with American President Donald Trump receiving criticism for his response to the tragedies.
Less than 24 hours after Imoden's protest, a second was then staged by Berry, following her victory in the women's hammer throw competition.
Berry was seen raising her right fist at the conclusion of her medal ceremony.
It mirrored the act of Olympic sprinters Tommie Smith and John Carlos at the Mexico 1968 Olympic Games, where the duo won gold and bronze medals in the 200 metre race.
The act was a civil rights protest against racial discrimination.
The Australian Olympic Committee last year awarded a posthumous Order of Merit to Peter Norman, who stood in solidarity with the black American athletes on the podium.
After Carlos had left his gloves at the Olympic Village, it was Norman, who came from a Salvation Army background, who suggested that the pair share Smith's to carry out a salute that Smith later clarified had been for human rights and not black power.
Both Imdoen and Berry are in breach of Panam Sports rules under a section on "advertisements and publicity during the development of the Pan American Games.
The rules state "No kind of demonstration or propaganda of any kind is allowed at the venues of the Games or at other sites or areas considered part of the Games."
The consequences of breaches in the relevant section state: "Any violation of the provisions of the present Section shall result in disqualification or withdrawal of the accreditation of the person or delegation concerned.
"The Panam Sports Executive Board may take further measures and/or impose further sanctions against the NOC or Pan American Sport Confederation and/or International Federation that are responsible of such 29 violation.
"The decisions taken by the Panam Sports Executive Board regarding this matter shall be final."
Panam Sports declined to comment when contacted by insidethegames.
United States Olympic and Paralympic Committee (USOPC) have said their leadership are reviewing the consequences that may result from the political protests.
“Every athlete competing at the 2019 Pan American Games commits to terms of eligibility, including to refrain from demonstrations that are political in nature," USOPC spokesman Mark Jones told insidethegames in a statement.
“In this case, Race didn’t adhere to the commitment he made to the organising committee and the USOPC.
“We respect his rights to express his viewpoints, but we are disappointed that he chose not to honour his commitment.
“Our leadership are reviewing what consequences may result.”
Imboden and Berry are not the first to express anti-Trump sentiment during the Games here.
American nine-times Olympic medallist and former men’s 100 metre world record holder Carl Lewis criticised the President during a press conference.
"We have a president who is racist and a misogynist, who doesn’t value anybody but himself," he said.
The issue has not been exclusive to Lima 2019, however, with women's football player Megan Rapinoe confirming that she would not visit the White House if the US were triumphant at the FIFA Women's World Cup, which they went on to win last month.
During the tournament, she refused to sing the national anthem in protest at a decision by US Soccer to ban players from kneeling during the anthem.
Her actions drew a response from Trump, who accused Rapinoe of "disrespect" in a series of tweets.
A municipal employee sprayed gunfire "indiscriminately" in a government building complex on Friday in the US state of Virginia, police said, killing 12 people and wounding four in the latest mass shooting to rock the country.
The shooter was also killed after an extended gun battle with responding officers, in a scene that "best could be described as a war zone", Virginia Beach police chief James Cervera said.
The shooting happened just after 4pm, when the gunman entered one of the buildings at the Virginia Beach municipal complex and "immediately began to indiscriminately fire on all of the victims", Mr Cervera said.
One victim was killed outside in his vehicle, while the others were found on all three floors of the building. Police raised the casualty toll to 12 dead and four wounded on Friday night, after earlier reporting 11 dead and six wounded.
Authorities did not immediately name the attacker but sources quoted by CNN identified him as DeWayne Craddock, a 40-year-old civil engineer who worked in the municipality's public utilities department.
Mr Cervera said the shooter was armed with a .45-calibre handgun fitted with a sound suppressor, and he reloaded several times with extended magazines. Officers were able to locate him from the sound of gunfire and "immediately engaged with the suspect", he said, adding "I can tell you that it was a long gun battle".
The wounded included a police officer, who was saved by his bulletproof vest. All were undergoing surgery on Friday night.
The building where the shooting took place in Virginia Beach – a city of 450,000 people about 320 kilometres south-east of Washington – housed the city's public works and utilities offices and could have as many as 400 people inside at any time.
"This is the most devastating day in the history of Virginia Beach," Mayor Bobby Dyer told reporters. "The people involved are our friends, co-workers, neighbors and colleagues."
Megan Banton, a public utilities employee, told local television station WVEC that during the chaos she and about 20 co-workers hid in an office, where they used a desk to wedge the door shut.
"We just wanted to try to keep everybody safe as much as we could and just trying to stay on the phone with 911, just because we wanted to make sure [police] were coming. They couldn't come fast enough," she said, adding that it felt like "hours".
"We heard gunshots. We kept hearing gunshots and we kept hearing the cops saying, 'Get down.'"
Ms Banton said it felt "surreal" to have a mass shooting in her office building, and having survived it she just wanted to go home and hug her family.
"I have an 11-month-old baby at home and all I could think about was him and trying to make it home to him," she said.
President Donald Trump had been briefed on the shooting and was monitoring the situation, the White House said.
According to the Washington-based Gun Violence Archive monitoring group, Friday's shooting was the 150th mass shooting in the United States this year, defined as a single event in which four or more people are shot or killed.
Despite the scale of gun violence across the nation, gun ownership laws are lax and efforts to address the issue legislatively have long been deadlocked at the federal level.
Among Democrats, the response to the shooting was especially pointed, with many of the party's White House hopefuls weighing in on the gun violence crisis.
"Another horrific shooting shocks the nation, this time in Virginia Beach," Pete Buttigieg tweeted. "Already, this much is clear: it is unacceptable for America to remain the only developed country where this is routine. We must act."
Senator Bernie Sanders decried the influence of the National Rifle Association, a powerful lobby group that routinely calls for more guns in US society so that ordinary citizens are armed and ready to confront a "bad guy".
"The days of the NRA controlling Congress and writing our gun laws must end. Congress must listen to the American people and pass gun safety legislation. This sickening gun violence must stop," he said in a tweet.
Virginia Governor Ralph Northam said it was a "horrific day" for the state.
"Our hearts ache over the senseless violence that has been inflicted upon the Virginia Beach community today. My deepest condolences and prayers go to the families of those who left home this morning and will not return tonight," he said.
Singer and music producer Pharrell Williams, a native of Virginia Beach, paid homage to the strength of his hometown.
"We are praying for our city, the lives that were lost, their families and everyone affected. We are resilient," he said in a tweet.
"We will not only get through this but we'll come out of this stronger than before we always do."