When reports first circulated on Twitter of a deadly attack by Israeli commandos on the Gaza flotilla, I didn’t forward them because they seemed implausible. I thought: Israel wouldn’t be so obtuse as to use lethal force on self-described peace activists in international waters with scores of reporters watching.

Ah, but it turned out that Israel could be so obtuse after all. It shot itself in the foot, blasting American toes as well, and undermined all of its longer-term strategic objectives.

Abba Eban, the former Israeli statesman, is famously reported to have said in 1973: “The Arabs never miss an opportunity to miss an opportunity.” The quotation resonated because it was largely true.

Palestinians were locked for years into a self-defeating dynamic of violence and self-pity that led to terrorism and intransigence. Feeling misunderstood, they shrugged at global opinion and lashed back wherever they could, undermining their own cause.

Yet now, as a rabbi noted on my Facebook page, it is Israel that never misses an opportunity to miss an opportunity.

Israel under Prime Minister Benjamin Netanyahu seems locked in a self- defeating dynamic in which it feels misunderstood and gives up on international opinion. It lashes out with force in ways that undermine its own interests. It is on a path that could eventually be catastrophic.

There’s no question that Israel faces existential threats. That should make its leaders focused above all on two things: an Arab-Israeli treaty and pressure on Iran to drop its nuclear program.

These aren’t easy, and a Palestinian-Israeli deal may be impossible for the time being. But Israel could freeze all settlements and take other steps that would make a deal more likely. We already know what the final deal would look like — a two-state solution and terms resembling the “Clinton parameters” that Bill Clinton proposed in 2000.

Israel could also cultivate Turkey, a central player in the effort to press Iran. Instead, Israel’s storming of a Turkish-flagged vessel in international waters was a huge setback to efforts to win new sanctions on Iran. One big winner in this week’s fiasco was the Iranian regime.

Israel is also antagonizing its support base in the United States, which is critical to protect it from those existential threats.

Peter Beinart wrote a powerful article in the most recent New York Review of Books exploring the way young Jews in America feel much less identification with Israel than their elders did. Mr. Beinart noted that even the student Senate at Brandeis University, which has strong Jewish ties, rejected a resolution commemorating the 60th anniversary of Israel.

One basic problem, Mr. Beinart said, is that the Zionist movement has become increasingly conservative politically. “For several decades,” he writes, “the Jewish establishment has asked American Jews to check their liberalism at Zionism’s door, and now, to their horror, they are finding that many young Jews have checked their Zionism instead.”

Israel’s hard-line policies are depleting America’s international political capital as well as its own. Gen. David Petraeus noted two months ago that the perception that the United States favors Israel breeds anti-Americanism and bolsters Al Qaeda. The chief of Mossad, Meir Dagan, was quoted in the Israeli press as making the point more succinctly: “Israel is gradually turning from an asset to the United States to a burden.”

For many Israelis, all this seems profoundly unfair. Israel is a thriving democracy that withdrew from Gaza but is still threatened by missiles from north and south alike. So Israel and its hard-core supporters tend to dismiss outside criticism as inherently unfair and anti-Semitic, and embrace unilateral solutions based on force. As the newspaper Haaretz suggested, Israel is now “lost at sea.”

How do we change this dynamic? One necessary step is a major investigation of what happened. Another is a quick end to the blockade of Gaza, by Egypt as well as Israel. The blockade has failed to topple Hamas, failed to recover the captured soldier Gilad Shalit, and failed to keep rockets out of Gaza.

When you visit Gaza, you see that the siege has accomplished nothing — except to devastate the lives of 1.5 million ordinary Gazans. Gisha, an Israeli human rights organization, has compiled a list of goods that Israel typically blocks from Gaza: notebooks, blank paper, writing utensils, coriander, chocolate, fishing rods, and countless more. That’s not security; that’s a travesty.

President Obama needs to find his voice and push hard for an end to the Gaza blockade. He needs to talk sense to Israel and encourage it to back away from its plans to intercept other flotillas now headed for Gaza — that would be a catastrophe for Israel and America alike.

Above all, he needs to nudge Israel away from its tendency to shoot itself in the foot, and us along with it.