A 40 Y/O man underwent laparoscopic cholecystectomy 2 years ago. He remains asymptomatic until 1 week before admission, when he complains of right upper quadrant pain and jaundice. He develops a fever and has several rigors attacks on the day of admission. U/S confirms the presence of gallstones in the distal CBD. The patient is given antibiotics. Which of the following should be undertaken as the next step in therapy?