1. President who wrote "Posterity! You will never know how much it cost the present generation to preserve your freedom! I hope you will make a good use of it" → ADAMS
2. Default outcomes, perhaps → REPOS
3. Kind of sequence that that proceeds 0, 1, 1, 2, 3, 5, 8, 13, ... → FIBONACCI
4. Duration → WHILE
5. Modern security threat → HACK
6. Org. with the Rule of Law Initiative → ABA
7. Cylindrical oven → TANDOOR
8. Extremely well-liked? → INTERNETFAMOUS
9. Personal opinion? → SELFESTEEM
10. Hooting and hollering → AROAR
11. Part of an underground network → ROOT
12. Pithy put-downs → TSKS
14. Main ingredient in an aviation cocktail → GIN
15. "I like the sound of that!" → NOWWERETALKING
20. "So adorable!" → AWW
24. Prepare to ship, say → BOXUP
26. Delivery means to a gas station → FUELTANKER
27. Count in the Blues Hall of Fame → BASIE
28. On the ___ (frequently, informally) → REG
29. Bird whose eggs are sometimes a canvas for Aboriginal art → EMU
30. Capotes are flapped at them → TOROS
31. "Let's go, sleepyhead!" → UPANDATEM
32. Booking, for short → RES
33. Server's obstacle → NET
38. "Word on the street is ..." → THEYSAY
41. ___ Brown, author of "The Da Vinci Code" → DAN
42. Night of lawlessness in a long-running horror franchise, with "the" → PURGE
43. Try-hard → POSER
45. Kind of acid → AMINO
46. Stem component → XYLEM
47. Capitulate → CAVE
48. Lender's security → LIEN
49. Table outside → MESA
50. Big purveyor of health supplements → GNC
52. Gender-neutral term in a family → SIB