Final answer:
The word that best fits the meaning of the sentence is 'unwavering'.
Step-by-step explanation:
The word that best fits the meaning of the sentence is unwavering. The phrase 'support for the causes that mattered to her district' suggests that the politician showed consistent, unwavering support for these causes. Being reelected for five consecutive terms indicates that this support was a significant reason for her success in Congress.
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