Question: who is the first president to be impeached
[{'answer': 'Johnson', 'provenance': [{'wikipedia_id': '9583338', 'title': 'Impeachment of Andrew Johnson', 'start_paragraph_id': 0, 'start_character': 22, 'end_paragraph_id': 0, 'end_character': 29, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'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.'}]}, {'provenance': [{'wikipedia_id': '9583338', 'title': 'Impeachment of Andrew Johnson', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10968551028997360797}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '9583338', 'title': 'Impeachment of Andrew Johnson', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 750, 'bleu_score': 0.7142450417019921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10968551028997360797}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '31756', 'title': 'United States Congress', 'section': 'Section::::Role in Government.:Checks and balances.\n', 'start_paragraph_id': 52, 'end_paragraph_id': 52, 'meta': {'evidence_span': ['Only two presidents have ever been impeached: Andrew Johnson in 1868', "Only two presidents have ever been impeached: Andrew Johnson in 1868 and Bill Clinton in 1999. Both trials ended in acquittal; in Johnson's case, the Senate fell one vote short of the two-thirds majority required for conviction.", "Only two presidents have ever been impeached: Andrew Johnson in 1868 and Bill Clinton in 1999. Both trials ended in acquittal; in Johnson's case, the Senate fell one vote short of the two-thirds majority required for conviction."]}}]}, {'provenance': [{'wikipedia_id': '19468510', 'title': 'United States House of Representatives', 'section': 'Section::::Checks and balances.\n', 'start_paragraph_id': 113, 'end_paragraph_id': 113, 'meta': {'evidence_span': ['Only two presidents of the United States have ever been impeached: Andrew Johnson', '(Another, Richard Nixon, resigned after the House Judiciary Committee passed articles of impeachment but before a formal impeachment vote by the full House.) Only two presidents of the United States have ever been impeached: Andrew Johnson in 1868 and Bill Clinton in 1998', "Andrew Johnson in 1868 and Bill Clinton in 1998. Both trials ended in acquittal; in Johnson's case, the Senate fell one vote short of the two-thirds majority required for conviction."]}}]}, {'provenance': [{'wikipedia_id': '9583338', 'title': 'Impeachment of Andrew Johnson', 'section': 'Section::::Abstract.', 'start_paragraph_id': 2, 'end_paragraph_id': 2, 'meta': {'evidence_span': ['Johnson became the first American president to be impeached', 'Johnson became the first American president to be impeached (the only one prior to Bill Clinton in 1999) on March 23, 1868']}}]}, {'provenance': [{'wikipedia_id': '47279701', 'title': 'Impeachment process against Richard Nixon', 'section': 'Section::::Abstract.', 'start_paragraph_id': 3, 'end_paragraph_id': 3, 'meta': {'evidence_span': ['The other twoAndrew Johnson in 1868', 'The other twoAndrew Johnson in 1868 and Bill Clinton in 1998were both impeached; however, both were also acquitted from all charges following a Senate trial, and thus allowed to remain in office.', 'Andrew Johnson in 1868 and Bill Clinton in 1998were both impeached; however, both were also acquitted from all charges following a Senate trial, and thus allowed to remain in office.']}}]}]