Two days ago the Syrian prime minister, Riad al-Hijab, a Sunni, defected to Jordan with a number of aides and a pilot. He had only been in office for two months and was not a key figure in the regime but was one of the few remaining figures from the Sunni majority as opposed to one of the religious minorities such as Alawites, from which the ruling Assad family comes, or Christians. Here is a link to an article on the defection from the Washington Post. This of course led to speculation about whom would be next to leap. But how will the defection affect the Assad regime's hold on power?
The defection might possibly serve to weaken Russia's support for the regime, as Russia has arms ties to Syria dating back to the mid-1950s before Bashar al-Assad's father Hafiz was even defense minister let alone the Syrian president. So Russia might decide that if the regime is unsustainable that it might attempt to make a deal with the opposition, particularly with some figure such as Manaf al-Tlas, another Sunni, who defected within recent weeks and was the son of Hafiz al-Assad's long-time defense minister. Of course, Tlas probably would not be acceptable to the religious fighters carrying out the revolution because of his playboy reputation and his previous support for the regime. But Assad's other main foreign backer, Iran, will not change sides because the Syrian link is contingent upon the sectarian nature of the regime. The Alawites are a heterodox offshoot of Shia Islam, which is the ruling religion in Iran. A Sunni regime would likely quickly break the link with Iran in exchange for ties with the mainstream Sunni Arab countries such as the Gulf states, Egypt, Jordan, and North African countries. In fact, today Bashar al-Assad was shown for the first time in weeks on Syrian television meeting with none other than an Iranian envoy.
After coming to power in early 1979 the Islamic Republic of Iran attempted to export its revolution throughout the Middle East and the Muslim world. It really only had much success in two countries: Lebanon and Syria. In Lebanon it sent 2,000 Revolutionary Guards who made contact with Shia militants in the Bekaa Valley in the early 1980s and founded Hezbollah. Hezbollah is the one great success story of the Iranian revolution. Syria formed an alliance of convenience with Iran based on mutual interests and sectarian identity rather than ideology. Syria provided a conduit for Iranian arms and instructors to Hezbollah in Lebanon and to Hamas and Palestinian Islamic Jihad, which both had offices in Damascus. Hezbollah was ideologically aligned with Tehran but had a client relationship with the secular Ba'athist regime in Damascus, which occupied Lebanon from 1976 to 2005.
After the Syrian revolution became widespread, Hamas broke with the regime and closed its offices in Damascus. It has since renewed relations with Jordan and established relations with the Muslim Brotherhood regime in Egypt--which is only natural as Hamas was originally an offshoot of the Egyptian Muslim Brotherhood. So both Tehran and Damascus are left clinging to each other in splendid isolation.