短语讲解：

1. These sanctions are a big reason why America was able to even bring Iran to the (negotiating) table in the first place.

be able to 能够
例句：He will be able to take up his normal routine shortly.
他不久就能处理日常事务。

2. The Senate Majority leader belongs to the Republican Party.

belong to 属于
例句：I belong to no party.
我不属于任何派别。

3. We know that it would be even more difficult to resolve our concerns about Iran's nuclear, Iran’s destabilizing activities, if Iran had a nuclear weapon.

concern about 关心，挂念
例句：She showed great concern about you.
她很为你担心。