Across:
8 Pose a question (-ASK-) after (= positional indicator) gangster (Al Capone = AL-) goes AWOL heading (‘AWOL’ heading = -A) (ALASKA) out of American State (ALASKA),
9 Verdi (Verdi) medley (= anagram indicator) (Verdi = DRIVE-) and track (-WAY) (DRIVEWAY) from a venue? (DRIVEWAY from a venue/place),
10 Snakes (ASPS) and newts removed from wasp’s nest (‘newts’ removed from ‘wasp’s nest’ = asps = ASPS),
11 Change of heart (TRANSPLANT) to move informer (plant) to the other side the border (move plant to other side of border = TRANSPLANT),
12 Seasonal worker (Christmas worker = DANCER) in Charleston (Charleston DANCE-) at the end of summer (at the end of ‘summeR’ = -R) (DANCER),
14 Cook (= anagram indicator) farm hens (farm hens = FRESHMAN) for a student of the first course presumably (first-year university student = FRESHMAN),
15 Aloof (FORMAL) Trim (s) characters in 22 across (‘complaints’ without ‘s’ = COMPLAINT) (FORMAL COMPLAINT) produced a letter of protest the authorities take seriously (FORMAL COMPLAINT),
18 Take (CAPTURE-) by director (-D) (CAPTURED) made into a movie perhaps (CAPTURED),
20 Let off the hook (EXEMPT) by former partner (EX-) and is mostly (y) unoccupied (‘empty’ without ‘y’ = -EMPT) (EXEMPT),
22 Criticisms (COMPLAINTS) of bone (-T- bone) in a number of beefs (beefs/complaints = COMPLAIN-S) (COMPLAINTS),
24 Figure (FORM) tries to get out of Firestorm (‘tries’ to get away from ‘firestorm’ = from = FORM),
25 Address (MISS-) leader heading off (v) offensive (‘vile’ without ‘v’ = -ILE-) with endless (end ‘lesS’ = -S) (MISSILES) sky-bound weapons (MISSILES),
26 Savannah’s (PLAINS) Spinal (Spinal = PLAINS) Tap? (= anagram indicator).
Down:
1 It’s in the blood (PLASMA) raising (= reversal indicator) sheepish types (rams) off the summit (r) (‘rams’ without ‘r’ = ams = -SMA) on mountain (alp = PLA-) (PLASMA),
2 Fundamentalist group (ISIS) imprisoned in Ellis Island (imprisoned in ‘EllIS ISland’ = ISIS),
3 New (= anagram indicator) patrols (patrols = PASTOR-L) around American border (‘American’ border = -A-) (PASTORAL) in rural area (PASTORAL),
4 Mental image (IDEA) of satin from East India (‘satin’ from ‘East India’ = edia = IDEA),
5 Bit of paper (TISSUE) with signatures doesn’t include Gran (‘signatures’ doesn’t include ‘Gran’ = situes = TISSUE),
6 Well, being (well-being = HEALTH CARE) in Wellington for instance (Wellington boot heel), by the sound of it (= homophone indicator) (‘heel’ = ‘heal’ = HEAL-), for half of them (for half of ‘THem’ = -TH) takes maintenance (CARE) (HEALTH CARE),
7 Keep up (MAINTAIN) with important (MAIN-) Irish legend (An Táin = -TAIN) (MAINTAIN),
13 Visited the great St Bernard, for instance (visited the great St Bernard Pass = CAME TO PASS), as it happened (CAME TO PASS),
14 What restaurants serve (F-OOD) around port (port/left= -L-) (FLOOD) in Rush when the heavens open? (rush with rain = FLOOD),
16 For either partner (“either or” = OR-) setting up (= reversal indicator) duty roster (rota = -ATOR-) at Number 10 (-IO) (ORATORIO) and providing work for the musicians (ORATORIO),
17 Exercises (PRESS-UPS) journalists’ (PRESS-) union (-U-) with pressure (-P-) on society (-S) (PRESS-UPS),
19 Without a doubt (REALLY), it’s a meeting (R-ALLY) about drugs (ecstasy = -E-) (REALLY),
21 Parliament dismisses mail (‘parliament’ dismisses ‘mail’ = parent = PARENT) from The Guardian (PARENT),
23 Sixth sense (NOSE) of North Vietnamese banks (‘NOrth VietnameSE’ banks = NOSE),
24 Phobia (FEAR) of some still-life artists (some ‘still-liFE ARtists’ = FEAR).