Abraham Lincoln was assassinated while he was in office. Andrew Johnson was his Vice president so he took over on April 15, 1865.
Andrew Johnson became president because Abraham Lincoln was assassinated.
No one influenced Andrew Johnson to become President. John Wilkes Booth assassinated Abraham Lincoln and Johnson succeeded him as President.
Abraham Lincoln died the morning of April 15, 1865 so Johnson took office later that day.
That day was April 15, 1865, the day that Lincoln died.