This won't directly affect the general election but the chain of events that follows might.
Tonight, Sanders is likely to say that the Iraq War which Hillary voted to authorize played a big part in the regional instability that helped foster the rise of ISIL. But she'll probably avoid damage.
The Iraq War has been litigated and Clinton has already stated that she regrets her vote.
If anything it might make the security-concerned voters to gravitate more towards her because of her experience as SoS.
