I saw Issa on Greta a little while ago, and he is going out of his way to soft pedal the situation - apparently for public relations purposes - while still moving forward to get the information he's seeking. He is saying he didn't subpoena Holder, but rather subpoenaed "documents", and has simply "invited" Holder to "clarify".
I would rather have a pitbull tearing chunks of flesh from this administration. But perhaps it is wise not to seem too eagerly out for blood.