Learn Polish: Zachwycamy się postawą tego polityka. - We are delighted with the attitude of this politician.

The verb zachwycać się (to be delighted with, to admire) belongs to a special group of verbs expressing strong emotional attitudes that directly govern the Instrumental case. You do not need a preposition to mean "with" here; the verb and the case ending work together to create that meaning.

Why is tego polityka in the Genitive case instead of matching the Instrumental case of postawą?

The phrase tego polityka means "of this politician." It modifies postawą to show whose attitude it is. In Polish, when a noun phrase expresses possession or relationship like this, it stays in the Genitive case regardless of the grammatical case of the noun it belongs to.

Does the word postawa only mean "attitude" in a psychological sense?

Not exactly. Postawa can mean literal physical posture, but in a figurative sense like this, it refers to a moral stance, a professional approach, or someone's principled way of behaving. It is stronger and more deeply rooted than just a passing mood.

What is the perfective equivalent of zachwycać się, and how would it change the sentence?

The perfective form is zachwycić się. Because zachwycamy się is imperfective, it describes our ongoing, continuous state of admiration. If you used the perfective, for example in the past tense as zachwyciliśmy się, it would mean we suddenly became delighted or were struck by his attitude at a specific moment.