Republicans have reason to hope here, and not just if Sanders runs. In 2008 Democrats of course had to hit the necessary litmus tests on issues, but they didn't need to compete to overly "out-liberal" the others, and those that tried (e.g. Kucinich) went nowhere. It's harder when you're the party out of power to not keep one eye constantly focused on November. There were enough big names in the mix that sticking to the basics of opposing the Iraq War and reversing Bush's economic policies (in a restrained-ish return to Clinton-era tax rates, etc.) was sufficient to remain credible and competitive.
This time around, though, the only way to run against Hillary (or Biden), or get noticed among the pack if she doesn't run, is to stake out a claim as the "true progressive" in the race. These forces are going to pull most Democratic contenders far more to the left than the 08 primary race did.
But this is of course all moot if Hillary runs.
