In an email to supporters, Totten lays out his case against Schuette very clearly:
This race is about giving Michigan families an advocate who keeps them safe and never lets politics get in the way. But it’s also about stopping a politician who is the most extreme, far-right Attorney General in the nation – a crusader who needs to be stopped now, before he does even more harm later.
In other words, we've got to stop him now before he tries to move up the ladder. Given Schuette's 30 years of running for public office (Congress, Legislature, Court of Appeals, Attorney General) it is assumed that reelection as Attorney General will be the start of his campaign for Governor.