Question: who was the last president of the us to be impeached
[{'answer': 'Bill Clinton', 'provenance': [{'wikipedia_id': '1795376', 'title': 'Impeachment in the United States', 'start_paragraph_id': 81, 'start_character': 10, 'end_paragraph_id': 81, 'end_character': 22, 'bleu_score': 1.0, 'section': 'Section::::Federal impeachment.:Federal impeachment investigations formally commenced and officials impeached.\n'}]}]