Complex sentence: Clinton's campaign ended up severely in debt; she owed millions of dollars to outside vendors and wrote off the $13 million that she lent it herself; the debt was finally paid off by the beginning of 2013.
Split into simpler sentences: Clinton's campaign ended up severely in debt; she owed millions of dollars to outside vendors and wrote off the $13 million that she lent it herself. The debt was finally paid off by the beginning of 2013.