Under which president were the 16th and 17th amendments passed?

In 1913, Taft signed both the 16th Amendment and the 17th Amendment to the United States Constitution.

Explanation:

https://ballotpedia.org/William_Howard_Taft#:~:text=In%201913%2C%20Taft%20signed%20both,to%20the%20United%20States%20Constitution.

I hope this will help you. ^^

four sitting presidents have been assassinated while in office but the first was abraham lincoln,

basic principles: federalism, separation of powers, checks and balances, judicial review, representative democracy, limited government, rule of law, individual rights and responsibilities, consent of the governed, majority rule, popular sovereignty, equal protection.