It looks like the Republicans threw every name on Obama's roster of cabinet designates into a hat and drew Eric Holder. And so, he'll be the guy they try to block.
I do think that blocking Eric Holder is crass and etc. But I don't think it's random. See, one of the very early questions that will face the Obama Administration is how to treat the crimes committed by the former Bush Administration. President Bush did not deliver any pardons, which means that an incoming Attorney General would be well within his rights to appoint a Special Prosecutor or in general open an investigation into, say, torture (along the Levin-McCain Report lines).
How can the Republicans in Congress possibly fight this? If they try to make a tough fight over Eric Holder, try and paint him as a partisan -- maybe leveraging his involvement in the Clinton Administration pardons -- they can then slander any attempt to bring President Bush or cabinet to justice as a partisan assault. They're hoping that they'll force Obama into the position of losing his mantle of bipartisanship, or forgetting any attempt to discipline the Bush administration.