The problem with that is the only way that a VP can be removed is by impeachment, death or resignation. I'm not sure that Harris would be willing to resign, even with the offer of becoming the AG.

The biggest stumbling block is that Garland has taken so long that once Trump announces (which will be soon), any investigation would seem politically motivated. I also read somewhere that historically, the DOJ does not investigate or prosecute preisdential candidates. I need to look into that further because if that is true, we are well and truly fucked.