The Fatah party, which Hamas defeated in recent elections, has long maintained good relations with Jordan, and the king of Jordan was not pleased with Hamas taking over the Palestinian government. Palestinian refugee families make up a large majority of the Jordanian population, and the king has to pay attention to Palestinian politics and public opinion. If Palestinians in Jordan become more pro-Hamas, that will create problems for the Jordanian government. So far, the Jordanians have been able to prevent a Palestinian take-over. But after three decades, the Palestinians are still a threat, and Hamas is the best organized and deadliest Palestinian terrorists the Jordanians have had to face in a long time.
This past Spring, Jordan arrested several Hamas members, and accused Hamas of planning terrorist attacks in Jordan. Hamas denied everything, but the incident was another chapter in the struggle between Hamas and the Jordanian government, that began in the late 1990s. Hamas insists, with some historical justification, that they do not attack anyone except Israelis. Officially, that's true. But Hamas extremists (even terrorist groups have extreme fringe elements) have turned up making attacks in Egypt, working with al Qaeda, and probably were planning attacks in Jordan.