As Mr. Obama made clear in his recent Middle East policy speech, the Quartet has not changed its view. "The recent announcement of an agreement between Fatah and Hamas raises profound and legitimate questions for Israel," he said. "How can one negotiate with a party that has shown itself unwilling to recognize your right to exist?"
Ephraim Sneh, a retired brigadier-general and former Israeli cabinet minister, rejects the idea of a long-term truce, or hudna. " Hudna, schmudna," Mr. Sneh said. "The long-term reality is that Hamas is never going to tolerate a Jewish state because it is against its religious beliefs."
Most Israelis, traumatized by dozens of suicide bombing attacks ushered in by Hamas in the 1990s and early 2000s, share his view. But some have begun to say that if peace is to be achieved, perhaps not all three of the Quartet's principles are necessary.
Efraim Halevy, a former director of Israel's Mossad intelligence organization, was among the first to advocate talking to Hamas. "They're not very pleasant people," Mr. Halevy said, "but they are very, very credible." He described the first two of the Quartet principles as "reasonable and imperative," but he said the requirement of recognizing Israel is "superfluous."
In mid-May, in the wake of the Palestinian factions' reconciliation, even Israeli President Shimon Peres said negotiations with Hamas should not be ruled out, though he indicated that Hamas should be willing to renounce terrorism.
Indeed, if Hamas ever is to be broadly acceptable as a negotiating partner or a recipient of Western assistance, it will have to convince Israel and the Quartet that it has ended its use of violence and especially the acts of terrorism with which it is so widely identified.
A history of violence
When the first Palestinian uprising, or intifada, began in the winter of 1987-88, Hamas organizers sent young men into the streets with stones to confront Israeli soldiers and tanks. It was a scene not unlike those now witnessed elsewhere in the Arab world where young people employ relatively non-violent tactics to confront military dictatorships.
But in the intifada, as Palestinian fatalities mounted and time wore on, stones gave way to firebombs, then to small arms.
By late 1992, Hamas's deadly hit-and-run operations against Israeli troops in the West Bank and Gaza had become so effective that Yitzhak Rabin, then the Israeli prime minister, had more than 360 Hamas leaders (along with about 50 Islamic Jihad personnel) rounded up and expelled through Israel's northern border.
It was in 1994 that Hamas first launched its campaign of suicide bombings targeting civilians inside Israel. The first such attack took place in Afula, in central Israel, when a 19-year-old bomber blew himself up at a bus stop, killing eight Israelis and wounding 34 others.
The date was April 6, exactly 40 days after an Israeli settler, Baruch Goldstein, a physician and reserve army officer, entered the mosque at Abraham's tomb in Hebron and killed 29 Palestinians at prayer, wounding dozens of others. That was the event, Hamas leaders say, that crossed "a red line" and changed the nature of the Israeli-Palestinian conflict.
Mr. Rabin was horrified by the attack. He called Yasser Arafat to offer personal condolences and saw to it that the extremist Kach party to which Dr. Goldstein belonged was banned.
It didn't matter: If Palestinian civilians at prayer could be attacked, Hamas reasoned, Israeli civilians would be considered targets too.
A week after the Afula attack, another bus was targeted in nearby Hadera, killing five Israelis. Six months later, 22 Israelis were killed by a suicide bombing on board a bus on Tel Aviv's busiest street. On and on the attacks went, throughout the mid-1990s, and again during the second intifada of the early 2000s.
Although Hamas officially denounced the tactic in 2005, many of its members still justify attacks on Israeli civilians. "When the Israeli planes hit a neighbourhood full of civilians because they want to arrest a wanted person and kill 30 or 40 people by using a one-ton bomb, isn't that excessive use of force?" asked Ayman Batniji, the imam at a major Gaza City mosque and spokesman for the Hamas police.
"So, when we send a person to perform an act of martyrdom [suicide bombing] and he wants to kill 10 or 20 Jews … we achieve advantages and pressure because we equate power with causing fear in others," Mr. Batniji said , sitting cross-legged on the floor as several wide-eyed young men looked on. "We don't have power, but we have the ability to strike fear."