In the latest TV series Scandal episode, "Get Out of Jail, Free", Olivia asks Mellie, a senator from Virginia, to release a prisoner imprisoned in Virginia, assuring that this is within her powers. I know this is just a TV series and even she might mean she has powerful friends or non-lawful tricks, but out of curiosity, is that possible or is there anything in US constitution or US law that let a senator get a prisoner out??
FYI, the senator did get two prisoners out, one imprisoned for embezzlement and another one for killing a president's son (and is put in Supermax!)