The most common and most likely answer to this crossword clue is the 10 letter word PRESIDENTS
I've seen this crossword clue in The Sunday Telegraph
P
R
E
S
I
D
E
N
T
S
Buddy explains!

The straight part
We know that "Powerful Americans" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case powerful americans = presidents.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRESIDENTS mean?
PRESIDENTS noun- An act in the past which may be used as an example to help decide the outcome of similar instances in the future.
- A decided case which is cited or used as an example to justify a judgment in a subsequent case.
- An established habit or custom.
- (with definite article) The aforementioned (thing).
- The previous version.
- A rough draught of a writing which precedes a finished copy.
- The head of state of a republic.
- In presidential republics, the head of government and head of state.
- Primary leader of a corporation. Not to be confused with CEO, which is a related but separate position that is sometimes held by a different person.
- A person presiding over a meeting, chair, presiding officer, presider.