Question: who's the first president to be impeached
[{'answer': 'Andrew Johnson', 'provenance': [{'wikipedia_id': '9583338', 'title': 'Impeachment of Andrew Johnson', 'start_paragraph_id': 0, 'start_character': 15, 'end_paragraph_id': 0, 'end_character': 29, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]