Answer: It doesn't.
In fact, the bigger Obama's lead, the better it is for them. Let me explain.
Lets assume they do try to steal the election. What talking points could they use?
1.) Polling is notoriously innaccurate. This election will prove once and for all that polling favours democrats, but the real vote doesn't reflect these obviously false polls. After they steal this one, they can put polling to rest forever.
2.) The "Bradley Effect" The obvious horse-shit about rascist voters...