He did not "invoke Executive Privilege"; he stated that internal communications from Justice to the POTUS are clearly covered by Executive Privilege to preclude "political witch hunts" and "interfere with responses to Congressional or Media Inquiries", as I recall.
Holder’s house-boy (Cummings) is making Statements and asking no questions so far, which prevents Holder from committing further Perjury, and now is lobbing softballs.