If the uprising succeeds in toppling Mr. Assad, the so-called "axis of resistance" would suffer a blow because the removal of a friendly regime in Damascus could end the weapons-supply link from Iran to Lebanon.
The axis of resistance already received a lesser blow in recent weeks, when Hamas abandoned its long-time patron Mr. Assad and relocated its headquarters from Syria to Egypt and Qatar, two Sunni states with stronger ties to the West.
"[The Arab Spring] changes the trend from an ascendency of Iran and its allies and its cronies to the decline and fall," says an Israeli diplomat who was not authorized to speak about the topic on the record. "Everybody was talking about the Shiite crescent. The Shiites are still there, but the Iranian dominance is flailing. They still wield influence over Iraqi Shiites, and Hezbollah, but there’s going to be a missing link if Assad falls."
To be sure, even though Iran's influence appears to be waning, Israelis worry that if Iran got a nuclear weapon, it could quickly regain that lost ground and be better able to project its power through the region.
That fear has added urgency to Mr. Netanyahu's efforts today in Washington to persuade Mr. Obama to define clear "red lines" for Iran's nuclear program.