ISTANBUL — Turkey sent tanks, warplanes and special operations forces into northern Syria on Wednesday in its biggest plunge yet into the Syrian conflict, enabling Syrian rebels to capture an important Islamic State stronghold within hours. The operation, assisted by American warplanes, is a significant escalation of Turkey’s role in the fight against the Islamic State, the militant extremist group ensconced in parts of Syria and Iraq that has increasingly been targeting Turkey. By evening, Syrian rebel fighters declared that they had taken control of the Islamic State stronghold, the town of Jarabulus and its surroundings, which had been the militant group’s last major redoubt near the Turkish border. Turkish officials said one rebel fighter was killed but no Turkish troops died. Thank you, Mr President!