Why didn't Hannibal hamlin take over whe Lincoln was shot?

Hannibal Hamlin, who served as Abraham Lincoln's first vice president, did not take over after Lincoln was shot because he was no longer in office at that time. Hamlin had been replaced by Andrew Johnson as Lincoln's running mate for his second term. When Lincoln was assassinated on April 14, 1865, Johnson, who had assumed the vice presidency, became president as per the line of succession established by the Constitution.