An Israeli soldier carries a shell at a mobile artillery unit while it fires towards the Gaza Strip. Israel declared a Gaza ceasefire over on Friday and killed more than 50 Palestinians in renewed shelling, saying militants had breached the truce after it began and apparently captured an Israeli soldier. (Baz Ratner/Reuters)

The collapse of a hard-won cease-fire in the Gaza Strip after only a few hours Friday lessens the already-limited American leverage to end Israel’s longest and most deadly war since President Obama took office.

It also opens the Obama administration to new criticism from Congress and pro-Israel organizations that the pressure put on Israel to limit civilian casualties is misplaced.

On Friday, the Senate quickly passed $225 million in new funding for Israel’s Iron Dome defense system that it had refused to approve the night before. As the House prepared to take up the measure before the five-week congressional recess begins Saturday, Sen. Lindsey O. Graham (R-S.C.) called on Obama and Secretary of State John F. Kerry to “knock off” their calls for Israeli caution.

In a sharply worded statement, the Emergency Committee for Israel said: “President Obama and Secretary Kerry must do more than denounce Hamas’s terrorist acts. Obama and Kerry must change course. They must stop pressuring Israel to stop fighting a just and necessary war.”

Obama blamed Hamas for the diplomatic collapse. He told reporters Friday that it will be hard to resurrect a cease-fire but that the United States will keep trying. More deferential to Israel than in past comments on the crisis, he was measured in his references to Palestinian civilian casualties.

“On the one hand, Israel has a right to defend itself, and it’s got to be able to get at those rockets and those tunnel networks. On the other hand, because of the incredibly irresponsible actions on the part of Hamas to, to oftentimes house these rocket launchers right in the middle of civilian neighborhoods, we end up seeing people who had nothing to do with these rockets ending up being hurt,” Obama said.

“Part of the reason why we’ve been pushing so hard for a cease-fire is precisely because it’s hard to reconcile Israel’s legitimate need to defend itself with our concern with those civilians.”

Kerry condemned what he called “outrageous” Palestinian violations of the truce, which he said flouted assurances given to the United States and the United Nations.

“After the horrific loss of life in this attack and its aftermath, it would be a tragedy if this outrageous attack leads to more suffering and loss of life on both sides of this conflict,” Kerry said.

That was as close as Kerry got to an admonition to Israel not to turn away from truce efforts completely or go overboard in retaliation.

With Israeli public opinion in grim unity that the Gaza operation is worth the loss of life and international criticism it has cost, Israeli Prime Minister Benjamin Netanyahu can afford to put off U.S. appeals for restraint. Netanyahu’s hand is strengthened by the coalescing of his fragile political coalition around the principle that Israel will do what it feels it must. The capture of an Israeli soldier is likely to harden Israeli resolve to keep going.

“It’s not becoming unsustainable. The Israeli public is completely unified, the Israeli government is unified,” said Middle East scholar Jon B. Alterman of the Center for Strategic and International Studies.

“The people who are most upset are people the Israelis have written off,” such as some European leaders, Alterman said.

The U.S. role in past conflicts has been to hold the international criticism at bay as long as possible and then to lean on Israel to scale back its operations when some tipping point was reached.

This time, Netanyahu has chafed at what looked like American moralizing or, worse, scolding. Kerry’s truce efforts, even before Friday’s aborted cease-fire, have been lacerated in the Israeli press, with senior government officials there doing little to mask their annoyance.

Kerry’s initiative came via direct orders from Obama, who suggested on July 21 that Israel had already done enough damage to Hamas and rued the death toll, which has more than doubled since then.

“Obviously, there are enormous passions involved in this and some very difficult strategic issues involved,” Obama said then. “Nevertheless, I’ve asked John to do everything he can to help facilitate a cessation to hostilities. We don’t want to see any more civilians getting killed.”

On Friday, Obama praised Kerry for trying but left little doubt that he is pessimistic about further efforts.

“Give John Kerry credit,” he said. “He has been persistent and worked very hard.” Kerry, Obama said, “has endured on many occasions really unfair criticism simply to try to get to the point where the killing stops and to try to get to the underlying issues. . . . We’re going to keep working toward that.”

But, he said, “I think it’s going to be very hard to put a cease-fire together again if Israel and the international community can’t feel confident that Hamas can follow through.”

Asked whether he felt that both the United States and its president had lost influence in the world, Obama was reflective.

“Look, this is a common theme that folks bring up. Apparently people have forgotten that America, as the most powerful country on Earth, still does not control everything around the world,” he said. “Our diplomatic efforts often take time; they often will see progress and then a step backwards. . . . That’s the nature of world affairs. It’s not neat, and it’s not smooth.”

Noting his success this week in rallying Europe to impose harsher sanctions on Russia, Obama said, “We have made progress on delivering what we said we’d do.”

Still, he said, “the point is that if you look at the 20th century and the early part of this century, there are a lot of conflicts America doesn’t resolve. That’s always been true. It doesn’t mean we stop trying. It’s not a measure of American influence at any given moment.”

Referring to Kerry’s unsuccessful efforts to bring Israel and the Palestinian Authority in the West Bank to fruitful negotiations earlier this year, Obama said his administration had “invested an enormous amount.”

“In the end,” he said, “it’s up to the two parties to make a decision. . . . You show them a path, but they’ve got to want it.”