Final answer:
The phrase 'seems like a no-brainer' best helps determine the meaning of 'habitual', highlighting that voter turnout is an expected, regular practice for individuals.
Step-by-step explanation:
The phrase that best helps the reader determine the meaning of 'habitual' as used in the context of voter turnout is 'seems like a no-brainer'. This phrase indicates that the action of voting is viewed as something that should logically and naturally be done, suggesting that doing it regularly becomes a habit. Thus, habitual voter turnout suggests that people regularly participate in voting, making the process a routine part of their civic engagement.