είναι ορατή διά
γυμνού οφθαλμού η προεκλογική σκοπιμότητα
the move doubtless had an air of political expediency.
The English is clearly here not a close translation of the Greek, but in a broader sense it preserves the meaning. is visible to the naked eye is certainly an accepted expression in English but would perhaps be too striking in English, where the literal sense is relatively common and the metaphorical sense of "obvious" not so common.
What the translator seems to be doing here is using "prefabricated" chunks of English to provide an easy-to-read text which conforms to the English reader's idea of how words "go together"
Notice too the different translation of σκοπιμότητα in the next paragraph. Can you think why the English translator might have wanted to change the word used?