The Arab awakening is stalking its next victim, King Abdullah II of the Hashemite Kingdom of Jordan, a key American ally. President Obama and his national-security team have another critical challenge.

Jordan is the invention of Winston Churchill. At the end of World War I, England needed to give their Arab Hashemite allies a reward for their loyalty in the fight against the Ottoman Turks. King Abdullah I was given the kingdom after Churchill drew its borders on a map in Cairo. It has always been a fragile place surrounded by stronger neighbors eager to eat it. Abdullah I secretly made peace with Israel. His grandson Hussein made it official, and his son Abdullah II keeps the peace.

For most of the last two years, the unrest in the Arab world simmered in Jordan, but never boiled. Like his father before him, Abdullah II often promised reform and changed prime ministers and spy chiefs constantly to buy off demands for real change. For decades, the Hashemites were written off as antiques who would not survive.

Now the country is boiling. Cuts in gas subsidies produced massive protests and riots across the kingdom—the worst riots in the country since Abdullah became king in 1999. Most important, for the first time, protesters called for the regime to fail. No more reform, just revolution.

The main opposition party is the Muslim Brotherhood, which has avoided calling for an end to the monarchy. The country is deeply divided between the Palestinians—refugees and their descendants from the West Bank, and their Hashemite counterparts from the East Bank.

A civil war in 1970 was won by the East Bankers and they control the army and the General Intelligence Directorate. The head of GID is the second-most-powerful man in the land. There are always an abundance of rumors about splits in the royal family. The Saudis and the Emirates have already intervened with force once to save the monarchy in Bahrain. The idea of an Arab king being toppled is their worst nightmare, but there are limits even to their money and power. Here in the Gulf the region looks to be exploding out of control and the royal palaces are deeply worried.

Obama should be worried too. Jordan is a key intelligence partner against al Qaeda, Iran, and in Syria. It has been a stable force for decades. It keeps the peace on Israel’s longest border. The king has escaped peril before, including an al Qaeda assassination plot. Like his father he is a survivor. But the Arab awakening is a formidable force.