They booed him saying the following:
Hillary is just as determined to defeat those who threaten us today: ISIS, al-Qaeda, Boko Haram, al-Shabaab. Terrorists who pervert the teachings of Islam to kill innocent people going about their daily lives, people traveling through airports in Brussels and Istanbul, families celebrating on the beachfront in France, men and women shopping in a market in Baghdad, and just this week, an 85-year-old priest whose throat was slit by terrorists who stormed his church during Mass. These murderers must be stopped.
The crowd booed stopping isil so stfu.