For a man whose trade was to keep people alive, he had certainly done poorly in his own family; and a bright doctor who within three years loses his wife and his little boy should perhaps be prepared to see either his skill or his affection impugned.
There are no more uses of "impugn" in the book.
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She impugns the statistics even though they are validated at factcheck.com.
Not being able to impugn her beauty, they attacked her costume.