How do I solve 23 down in Daily Telegraph Cryptic 31256?

Question

Accepted Answer

23 down reads "Support black mark involving the States" (7 letters); the answer is SUSTAIN. It's an anagram clue: the answer is a rearrangement of letters supplied by the clue itself. Look for an indicator like 'mixed', 'broken', 'cooked', or 'wild', and find a phrase whose letters add up to the answer's length. The full step-by-step breakdown is on this page.

Support black mark involving the States (7)

23D — Support black mark involving the States (7) — SUSTAIN