What does the cryptic crossword clue "CPGB regret a mix-up with a candidate from outside (12)" mean?

The wordplay uses an anagram. anagram of CPGB + REGRET + A + A = CARPETBAGGER The answer is CARPETBAGGER.

CPGB regret a mix-up with a candidate from outside (12)

Times Cryptic #29052 | 23 Across | 2024-10-19 flower