It's time to start thinking about what will happen to Israel - and U.S. policy in the Middle East - when the peace process ends.

Politicians don't openly discuss the deep threat to Israel's existence that would result from an end to negotiations over a two-state solution (meaning a Palestinian state living peacefully alongside Israel).

Instead, the Obama team calls for a revival of moribund peace talks - but it is merely going through the motions. The White House is too distracted to provide the necessary involvement, and the current Israeli government has no interest in talking substance. Meantime, divided and weak Palestinian leaders are trying to rally a U.N. vote for statehood in September that won't change much on the ground.

And so we drift toward the time when a two-state solution will no longer be possible, as Israeli settlements expand on the West Bank, and publics on both sides weary of diplomacy.

Last week, I heard a group of dovish Israelis with extensive military and diplomatic expertise describe the dangers the end of the two-state formula pose to their country. They deserve to be heard.

"This moment in Israeli history is more critical than ever that we end this conflict because time is running out for those who want to secure a democratic, Jewish state," said Gilad Sher, who served as chief of staff to Prime Minister Ehud Barak during the Oslo peace negotiations.

"The current situation is unsustainable," he said, speaking at the Woodrow Wilson Center in Washington. "If we discontinue the peace process, either we have an apartheid state or a Jewish-Palestinian state."

Sher was referring to demographic facts that pose an existential threat to the Jewish state, if it retains effective control over Gaza and continues to occupy the West Bank and Arab sectors of Jerusalem. Within that geographic area of "greater Israel," Jews hold a narrow edge in numbers over Palestinian Arabs. According to Sher's colleague, Shlomo Gazit, a former head of military intelligence, the percentage of Jews in greater Israel is 52 percent, and Arabs 48 percent.

This means that, if the peace process ends, Israel faces two highly undesirable choices: rule over an unwilling, largely disenfranchised Arab population, which produces the apartheid analogy, or give citizenship to all Palestinian Arabs, and lose the Jewish character of the Israeli state.

In the Middle East, where group loyalty trumps the American idea of citizenship, a "one-man, one-vote" solution wouldn't work; it would inevitably lead to further bloodshed. Palestinians and Israeli Jews deeply desire their own independent homeland.

But an apartheid state, where a bare Jewish majority eventually becomes a minority and rules over millions of Palestinian Arabs, is anathema to Israeli Jews who want a democratic homeland.

That's why Gazit calls demography "the number one threat to Israel," greater than the dangers posed by terrorism, rockets, or Iran. The latter, he believes, can be handled by Israel.

However, permanent rule over the West Bank and Gaza would destroy Israel's democracy. And - critically important - it would delegitimize the Israeli state abroad.

These men are deeply worried that the passage of time does not favor Israel. The status quo - in which West Bank terrorists have been crushed, with cooperation from the Palestinian Authority - is comfortable to most Israelis. As Jewish settlements and roads expand across the West Bank and East Jerusalem, a viable Palestinian state becomes less likely.

"A two-state solution at some point will no longer be seen as viable by Palestinians," said Alon Pinkas, a former foreign-policy adviser to Barak. "What are we going to do then?"

Pinkas also raised the prospect of Palestinians conducting huge, peaceful marches after a vote at the United Nations - a strategy now called for by their leaders, in the spirit of Egypt's Tahir Square revolution. "If they carry pictures of [Mohandas] Gandhi, not suicide bombers, what will we do then?" he asks.

An end to peace talks could undermine Israel's treaties with Egypt and Jordan. Jordan's monarch and Egypt's still-powerful military want to keep those treaties, but new popular pressures in both countries will make that more difficult if there is no movement toward a Palestinian state.

These Israelis are not novices in the hard world of Middle East politics. They know the risks a Palestinian state will pose to Israel, even if it's demilitarized, but they feel the alternative poses greater risks.

So do they see any way out?

They are part of a nonpartisan political movement called Blue White Future, whose founders include Sher and Ami Ayalon, former head of Shin Bet, the Israeli security service. To promote the two-state solution, the group is trying to facilitate the relocation of Jewish settlers from the West Bank to homes inside Israel.

But as to the bigger picture, a shift in Israel's approach is unlikely under Prime Minister Benjamin Netanyahu, they say, even as America's influence in the region is weakening.

The men point out that in the past, it has often taken an unexpected and dramatic event to change the approach of the parties - and perhaps prod an American president to take a more active role.

"I believe we wouldn't have reached peace without the 1973 war," says Gazit, "and the Oslo peace talks required the first [Palestinian] intifada" to jolt the sides into negotiations.

Such unexpected events can cut both ways: If a U.N. resolution in September is met with huge Palestinian demonstrations, Gazit fears Israel might overreact harshly, prodding a third intifada.

It would be far better if movement occurred because all sides recognized the status quo was unsustainable. Failing that, we can only wait for the unexpected, and hope.