Crossword Genius

Vow broken by Reagan briefly showing resolve (4,4)

Ross

I believe the answer is:

iron will

'resolve' is the definition.

'vow broken by reagan briefly' is the wordplay.
'vow' becomes 'iwill'.
'broken by' is an insertion indicator.
'reagan briefly' becomes 'ron' (Ronald Reagan).
'iwill' enclosing 'ron' is 'IRON WILL'.

'showing' is the link.

(Another definition for iron will that I've seen is " Steely determination, not to be deflected".)

I've seen this clue in The Guardian.
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