Democratic presidential nominee Joe Biden vowed to create a task force to reunite more than 500 children who were separated from their families at the U.S.-Mexico border by the Trump administration and whose parents have not been located. Under Republican U.S. President Donald Trump thousands of children were separated from their parents at the border, mostly in 2017 and 2018, because their parents were being prosecuted for illegal entry or over concerns about their identities or criminal histories. Separations happened both before and after Trump unveiled a “zero tolerance” policy to prosecute all illegal border crossers in May 2018, only to quickly reverse it after an international outcry. The American Civil Liberties Union sued over the matter in 2018 and U.S. District Judge Dana Sabraw in San Diego, California, ordered the families be reunited. There are around 4,000 children who could fall under the reunification order, but as of Oct. 20 parents of 545 children could not be reached by attorneys and non-profits searching for them, according to a court filing in the San Diego case. “On his first day as President, Joe Biden will issue an Executive Order creating a federal task force to reunite these children with their parents,” the Biden campaign said. Trump and Biden clashed over the issue during the final head-to-head debate last Thursday, ahead of the Nov. 3 election. Asked whether he had a plan to reunite families, Trump said: “Yes, we’re working on it.” The Trump campaign did not immediately provide a comment on Biden’s move. According to the ACLU, approximately 1,400 additional children were separated by the Trump administration but are not currently covered by Sabraw’s reunification order. ACLU attorney Lee Gelernt said there are hundreds of parents who have been located in Central America but have not been allowed to return to the United States to reunite with their children.