Historical clue formulations

• Subj. of the 17th Amendment — 2021-02-20
• Subj. of Article I, Section 3 of the Constitution — 2020-03-01
• Grp. that no one under 30 can join — 2019-05-24
• Wicker seat place? — 2013-02-15
• George J. Mitchell once led it — 2002-07-13
• Whip's place — 2002-02-16