Landlord interrupting about celebration for US political group (10,5)

I believe the answer is:

republican party

I'm a little stuck... Click here to teach me more about this clue!

'us political group' is the definition.
I can't tell whether this defines the answer.

'landlord interrupting about celebration for' is the wordplay.
'landlord' becomes 'publican' (as in a pub landlord).
'interrupting' means one lot of letters goes inside another.
'about' becomes 're' ('re' means regarding or about).
'celebration for' becomes 'party' (I can't explain this - if you can you should believe this answer much more).
're'+'party'='reparty'
'publican' put into 'reparty' is 'REPUBLICAN PARTY'.

Can you help me to learn more?

(Another definition for republican party that I've seen is " right across pond".)

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app