Canadian income earned and effect on US Social Security

Hello I have a question as follows:

- I am Canadian who has worked in the US for 15 years. I will be retiring and am eligible for SS benefits.

- I understand that as I am collecting SS I must complete a US tax return prior to submitting my Canadian tax return.

Question: What do I need to claim on the US tax return as income ?

- as the only "US sourced" income is my Social Security, is this all that I need to claim on

my US tax return as income ? I assume that I do not need to identify "Canadian sourced" income such as RRSP income, employment income ?

I assume that "US sourced" income such as SS is taxed in the US and "Canadian sourced" income is taxed in Canada ??? Is this correct ? Also, a related question, if my assumption is correct and I work full time back in Canada, will employment income earned in Canada affect my Social Security benefit amount ?

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