They both have equal strength: nil. Conyers' effort was symbolic and if a Republican introduced an impeachment bill it would get way more than 38 co-sponsors. There was never any plausible effort to impeach Bush.
Farenthold is a random junior backbencher talking out of his ass. John Conyers, the ranking member on the Judiciary Committee, an important member of House leadership, actually introduced a resolution that got 38 co-sponsors, including other influential Democratic House leaders. I think it's extremely clear that, at least as yet, the movement to impeach Obama has nowhere near the strength that the movement to impeach Bush did.
