The verb whiten in line 1 is a very compressed image. It means that the wind turns the white underside of the willow leaves upward. In line 2, dusk is used in an unusual way. What is its meaning? to become or make dark or dusky tending to darkness; dusky the darker stage of twilight, especially in the evening

Delegates: representatives who cast votes at a political party's national convention. binding: if a primary or caucus is “binding” that means the delegates won in that contest are legally bound to vote for a particular candidate at the parties national convention.a primary is a preliminary election used to determine a party's nominee for a specific office. the winner of the party's caucus, or primary, wins the party nomination for that state. then the delegates meet at their party's national party convention, which is a formal gathering of all party delegates from all states.