Nationalist working with editor is totally perplexed in America (9)

I believe the answer is:

nonplused

'totally perplexed in america' is the definition.
(US term for perplexed)

'nationalist working with editor' is the wordplay.
'nationalist' becomes 'n' (abbreviation in politics).
'working' becomes 'on'.
'with' becomes 'plus'.
'editor' becomes 'ed'.
'n'+'on'+'plus'+'ed'='NONPLUSED'

'is' is the link.

I've seen this clue in The Guardian.

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