Theme: Shocking - This isn't a case of adding the first word to the unifier; they are the unifier. They are events that can happen to an electric current.
20A. Add a little gin to a party drink, say : SPIKE THE PUNCH. A spike is a very short increase in the electrical supply voltage, current or both. It is why we have surge protectors on our computers.
25A. Game requiring full 25-square coverage to win : BLACKOUT BINGO. Don't be surprised if we have blackouts this summer. Temperatures in the 80's already around here.
46A. Efficient, wordwise : SHORT AND SWEET. A short has some quite technical definitions but in short,(sorry) it is current going where it shouldn't.
52A. Front page staple, and, in a way, what 20-, 25- and 46-Across begin with : CURRENT EVENTS
Argyle here and, by my count, Jeff Chen's fourteenth Monday puzzle and another winner. I'm sure some may find a nit here or there but they will be small and varied.
1. Pound of poetry : EZRA. There are some interesting quotes about him in this Wikipedia article.
5. Hourglass trickler : SAND
9. Salami and turkey jerky, e.g. : MEATS
14. Steak and hamburger, e.g. : BEEF. No tofu.
15. Je ne sais __ : QUOI. I can't describe it.
16. "That's plenty for me" : "I'M SET". Things I say when offered tofu.
17. Chicago footballer : BEAR. Mike Ditka comes to mind.
18. Sputnik launcher : USSR
19. Girl who says "Uncle" : NIECE. Cute clue.
23. KGB counterpart : CIA
24. Like puppies and kittens : CUTE. Cute answer.
31. Lao Tzu's "__ Te Ching" : TAO
32. "Smoke Gets in Your Eyes" composer Jerome : KERN. Timi Yuro clip.(2:19)
33. Item in a squirrel's stash : ACORN
35. Sandwich rolled in a tortilla : WRAP
37. Fix, as worn brakes : REPAD. Around the shop, they'll tell you they had to replace the pads(and rotors and calipers) but not they had to repad your brakes.
40. Europe's highest active volcano : ETNA. Another view.
41. Leading the league : ON TOP
43. Prefix with -syncrasy : IDIO
45. Cut the grass : MOW
50. Minnesota's "crazy" state bird : LOON. Insert loon stories here.
51. Bubble wrap filler : AIR
58. Salami type : GENOA. OMG, they make tofu salami. (see below)
59. "Dang it!" : "OH, NO!"
60. Lake south of Niagara Falls : ERIE
62. Ignoramus : IDIOT
63. "Ouch!" : "YEOW!". 67A. Youngster : TYKE. 44D. Baby's boo-boo : OWIE. 47D. Baby's "piggy" : TOE
64. It may lose its mate in the laundry : SOCK
65. "Please, I'll do that" : "LET ME"
66. Cheeky behavior : SASS
1. Flow back : EBB
2. Puzzle pair? : ZEE's. (middle letters)
3. Bring in from the field : REAP
4. Chad's continent : AFRICA. Atlas.
5. Tight game : SQUEAKER
6. Vienna's country: Abbr. : AUST. (Austria)
7. Small snack : NOSH. Yiddish.
8. Lead the orchestra : DIRECT
9. Trifling matter : MINUTIA
10. Cardinal's honorific, after "Your" : EMINENCE
11. Words after gimme or wait : A SEC
12. Georgia __ : TECH. The Yellow Jackets of Atlanta, Georgia.
13. Jeanne d'Arc, for one: Abbr. : STE.
21. Punt, say : KICK
22. Brit's watering hole : PUB. Quiz: Where does the word PUB come from?
25. Some owls' homes : BARNS. And some live in The Owlery on the top of Hogwarts Castle's West Tower.
26. Averse : LOATH
27. Precious metal source : ORE
28. Let down, as one's hair : UNPIN. Reminds me of this song which I haven't heard in awhile, so here it is. Clip.(2:32)
29. "I haven't a clue" : "GOT ME"
30. "... but then, I could be wrong" : "... OR NOT"
31. Bill featuring Jefferson : TWO
34. "Don't reckon so" : "NAW". Too many quotes...naw.
36. Where to see sharks with cues : POOL ROOM
38. Sum up : ADD
39. Denies knowledge of : DISAVOWS. CYA
42. Divide according to ownership : PRORATE
48. Rankles : ANNOYS
49. Author Hemingway : ERNEST. Did you see his quote about Ezra Pound?
52. Formally turn over : CEDE
53. Military group : UNIT
54. Ellington/Strayhorn's "Take __ Train" : THE 'A'. Taking it literally. Clip.(3:00)
55. Grandson of Eve : ENOS
56. City fooled by a horse : TROY
57. Ailing : SICK
58. Hodges of the Dodgers : GIL. But he managed the New York Mets to the 1969 World Series title, one of the greatest upsets in Series history.
61. Squeeze (out), as a living : EKE