Historical clue formulations

• "This ___ to do the trick" — 2021-09-20
• "There ___ to be a law!" — 2018-05-14
• Need (to) — 2016-01-10
• Moral obligation — 2010-03-12
• Should, with "to" — 2003-07-09
• Is expected (to) — 1999-12-09
• Word of obligation — 1998-09-09
• Should, with "to" — 1998-03-30