It is most likely that Turkey will accuse the Islamic State terrorists or the PKK militants. In both cases, the source of the threat will be found on the territory of Syria, which will encourage the Turkish authorities to invade the country. After yesterday's terrorist attack, such actions will now receive the support of Turkish society. Erdogan said that, in response to the terrorist attack Turkey, they would use their right to self-defense.
The United States rushed to support its NATO ally. According to US representative of the National Security Council Ned Price, the United States will provide unconditional support for Turkey.
Earlier, the USA strongly opposed attacks on the positions of Syrian Kurds by Turkish artillery. Now, in the Turkey-PKK conflict, it has become more difficult to support the Kurdish side, if Turkey decides to accuse it of the attack. At the same time it increases coordinated actions of the USA and Turkish in northern Syria, which would be justified as a counter-terrorism operation. This may be a full-fledged invasion or mainly special services and air operations.
The main objective of Turkey and the USA’s geostrategically speaking is to block the Turkish-Syrian border and to stop the advancement of Syrian troops, who are supported by Russia and Iran. Otherwise, allied Islamists will be surrounded and destroyed. A possible Turkish invasion is used to blackmail Russia, Iran and Syria, but it can only happen in reality if the other levers of pressure on US’ opponents do not work.