President Joe Biden, whose elder son died of cancer after serving in Iraq, signed legislation on Wednesday expanding federal health care services for veterans who served at military bases where toxic smoke billowed from huge "burn pits." "So many of you here today remind us that we have fought for this for so many years," Biden said during an emotional White House ceremony that reflected the struggles of military families — and the president's personal experience. Biden was introduced by Danielle Robinson, the widow of Sgt. 1st Class Heath Robinson, who died of cancer two years ago. The legislation is named for him.