Cryptic crossword No 3,983

Across

1. Demote envoy after Republican assumes leadership (8)
2. Offspring guitarist’s total happiness to begin with Rush’s singer (4,6)
3. Ancient city in South America (4)
4. Assassin M indicated is showing on your radar (2,4)
5. Aim for something very special! (3,2,1,7)
6. Apprentice story introducing new number: European yodeler's song (10)
7. Stoic butcher offers gun inside fish (4-9)
8. Nervous Nellie following addict around the middle of Bristol (6)
9. Jerk echoes loudly: Fourth of July - Assimilate! (8)
10. Machiavellian primarily influencing a gullible Othello (4)
11. On vacation, Sylvester, Lenny and I cause crashes for no reason (13)

Down

1. ______ _______ i.e., sky omen (6,7)
2. With a lilting voice, son gigs New York freely (9)
3. Snub kiss and cancel out-of-bounds pest (8)
4. Weird mansion keeping one in sleeplessness (8)
5. Prophet and old priest accompanying Supreme Being of Rastafarianism (6)
6. Dummies occasionally upset Big Bird (3)
7. "To Sir: I surrender." (embraces God) (6)
8. Newly born tale Nona’s concocted (8)
9. Direct is, for Gennaro, the elevated approach (6)
10. Instant caught in moving pictures (3)
11. Allegorical commonwealth borne from first person escaping Orwellian hellstate (6)
12. Calligrapher's tool used for mixing tattoo's hue (8)
13. Complimentary lay involving eccentric art duo (9)