Marilyn Davenport is resisting calls for her resignation from the Republican party's central committee after sending out the 'family portrait' with the statement: 'Now you know why – No birth certificate!'

She said it was a 'joke' made in reference to the conspiracy theory that Mr Obama is ineligible to be president because he was born outside America.

Scott Baugh, chairman of the Republican Party of Orange County, where Ms Davenport is an official, is calling for an ethics investigation.

'It’s just highly inappropriate, it’s a despicable message, it drips with racism and I think she should step down from the committee,' he said.

Ms Davenport has since apologised to party members in an email.

Marilyn Davenport is resisting calls for her resignation from the Republican party