If the is runoff is Schiff vs another Democrat, the second Democrat will win because the Republicans will vote for her to block Schiff.
This is entirely possible with Porter as well - she'll have to drive a distinction between her and Schiff, which means running to his left for the duration of the general campaign. I can't see her picking up too many Republican votes. I think the Republican vote is likely to drift away from Schiff, but it's also likely to be heavily depressed in any scenario because all four of these possible candidates are anathema to their base.
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