WASHINGTON — President Biden has been using a CPAP machine to treat sleep apnea, a potentially serious condition in which breathing can stop during sleep, the White House confirmed Wednesday. Administration officials acknowledged Biden’s condition and use of the device to Bloomberg News after journalists began asking for comment on strap lines visible on the president’s face while he gaggled with reporters on the White House lawn in the morning. Biden, 80, is the oldest-ever US president and is seeking a second term in next year’s election, despite concerns about his physical and mental fitness for office.