...The two attacks on opposite sides of Africa are among the scores of violent episodes to shake the continent in what experts are calling a breakout year for extremist groups affiliated with al-Qaeda or the Islamic State. .... The spike in terrorist attacks mirrors a steady, if less dramatic, increase in Islamist violence in parts of Syria and Iraq, driven by Islamic State fighters who slipped away after the caliphate’s defeat and have now regrouped.... The resurgence threatens to undermine one facet of President Trump’s reelection pitch to voters: his oft-repeated claim of victory over the Islamic State. ...The rise...