Republican helping after president's lapse (10)
I believe the answer is:
aberration
'lapse' is the definition.
(I've seen this before)
'republican helping after president's' is the wordplay.
'republican' becomes 'R' (political abbreviation).
'helping' becomes 'ration' (a ration is a serving or helping).
'after' says to put letters next to each other.
'president' becomes 'Abe' (Abraham (Abe) Lincoln).
'r'+'ration'='rration'
'rration' put after 'abe' is 'ABERRATION'.
(Other definitions for aberration that I've seen before include "Deviation from normality" , "irregularity" , "moral lapse" , "instability" , "mistake" .)