Trump cannot make his announcement tomorrow. He's had no problem using past terror attacks to bolster his claims, grabbing/sharing headlines from terror attacks, along with Ann Coulter.
This time, he doesn't want to share the headline with his veep choice. Pence is already arriving in NYC, but no announcement Friday AM as planned. Citing the terror attack.
This could hurt him - without the credibility of Pence, more on the RNC rules committee may be willing to let that new "good conscience" rule slide.