Joe Biden seemed to ask if a congresswoman killed in a car crash was in the crowd during a speech.
The US leader named Republican Jackie Walorski while thanking lawmakers from both parties for their efforts in helping his plan to end hunger in the United States by 2030.
During his speech during the White House Conference on Hunger, Nutrition, and Health in Washington DC, he asked if the congresswoman was in the crowd, saying "Jackie, are you there? Where's Jackie?"
Biden, 79, then went on to say: "She must not be here".
Jackie Walorski was 58 when she died along with three others in a head-on collision on August 3, 2022 when returning from a ribbon-cutting ceremony in Claypool, Indiana.
Biden released a statement after her death at the time and announced that White House flags would fly at half-staff in her honour.
Congress representatives have now demanded President Biden issue an apology to her family, reports the MailOnline.
Republican Vicky Hartzler said: "Truly an awful and disgraceful blunder.
"Jackie was a selfless leader and a dear friend. Her family deserves better than this. Biden and the entire White House staff should apologize."
Congressman Andy Biggs tweeted a clip of the video alongside the caption, "Your daily reminder that Biden is mentally unfit to be the President of the United States."
Biden's statement at the time of Walorski's death read: "Jill and I are shocked and saddened by the death of Congresswoman Jackie Walorski of Indiana along with two members of her staff in a car accident today in Indiana.
"Born in her beloved South Bend as the daughter of a meat-cutter and firefighter, she spent a lifetime serving the community that she grew up in – as a journalist, a nonprofit director, a state legislator, and eventually as a Member of Congress for the past nine and half years.
"We may have represented different parties and disagreed on many issues, but she was respected by members of both parties for her work on the House Ways and Means Committee on which she served.
"She also served as co-chair of the House Hunger Caucus, and my team and I appreciated her partnership as we plan for a historic White House Conference on Hunger, Nutrition, and Health this fall that will be marked by her deep care for the needs of rural America.
"We send our deepest condolences to her husband, Dean, to the families of her staff members, Zachery Potts and Emma Thomson who lost their lives in public service, and to the people of Indiana's Second District who lost a representative who was one of their own."
The latest blunder comes amid growing speculation around the mental health of the US president.
Last week, Biden appeared appeared to get confused and lost his way as he exited a stage at the Global Fund Conference as applause erupted.
As the president exits the stage, he appears to stop in his tracks before peering around looking a little confused.
Biden then briefly speaks to people in the audience before taking a few further steps.
Many described the scene as worrying, with critics saying Biden appears "lost".
Texas Senator Ted Cruz said the incident was "terrifying" on Twitter, with Cruz's communications adviser Steve Guest tweeting: "Joe Biden is completely lost on stage. Scary and sad."
