Remains round America? That's catastrophic (7)

I believe the answer is:

ruinous

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'catastrophic' is the definition.
(synonyms)

'remains round america?' is the wordplay.
'remains' becomes 'ruin' (I can't explain this - if you can you should believe this answer much more).
'round' becomes 'o' (o is a circular letter).
'america?' becomes 'U.S.' (United States).
'ruin'+'o'+'us'='RUINOUS'

'that's' acts as a link.

Can you help me to learn more?

(Other definitions for ruinous that I've seen before include "Devastating - dilapidated" , "far too expensive" , "Tumbledown - expensive" , "Broken down" , "Catastrophic" .)

I've seen this clue in The Daily Express.

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