import re

regex = r"(NP_\w+)(?: \([^()]+\))? is (NP_\w+)"
test_str = "NP_The_Eleventh_Air_Force is NP_a_Numbered_Air_Force of NP_the_United_States_Air_Force_Pacific_Air_Forces (NP_PACAF)."
matches = re.search(regex, test_str)

if matches:
    print(matches.group(1))
    print(matches.group(2))