“If Holder refuses to refer the Congressional referral to a federal grand jury, then he has set himself up for impeachment.”
The House can hold Holder in contempt and impeach him as much as it want. The Senate will never convict. Even if the Republicans win the Senate in 2014, the Senate will never convict Holder or most members of the current administration, including the President.
Impeachment is a political act. If any rats don’t vote to convict the criminal Holder, use it in the upcoming elections.