Lucy Wambui first suspected she was HIV-positive in 2000, when her baby fell ill and died. At the time, treatment for the virus was too costly for many families in the Kenyan town where she lives, 120 miles (193 kilometers) from Nairobi.

"People used to sell their land to buy medicines,” she recalled. It wasn’t until 2011 that she began antiviral therapy, thanks to free drugs available through the U.S.-funded President’s Emergency Plan for AIDS Relief, or Pepfar.

Today, Wambui has two healthy teenagers and her infection is well controlled. But new policy priorities under U.S. President Donald Trump have cast fresh doubt over the future of Pepfar — and the lives and health of 20 million people across 55 countries who depend on the program started in 2003 by former U.S. President George W. Bush.