The question of whether mediators matter took on acuity this weekend with the resignation of U.S. Mideast envoy George Mitchell, a move that came exactly as the Israeli-Palestinian conflict he was asked to help resolve seems about to retake center stage.

For all the hand-wringing in diplomatic circles, reaction on the ground in the Middle East itself, was uncharacteristically muted.

That reflected the fact that peace talks have been largely frozen since 2008, with the exception of a brief span in September, a Mitchell-mediated effort that quickly ran aground.

It may also have had to do with Mitchell's failure to truly get his groove with these rough-and-tumble protagonists: He was an envoy of the type who listens and facilitates — not the kind who takes a position and twists arms.

But some say that Mitchell — skilled and experienced, with a Northern Ireland peace deal to his credit — was impeded by the fact that the current crop of Israeli and Palestinian leaders simply wasn't ready.

The idea, in a wider sense, is that middlemen cannot do magic: for a deal to be possible, the stars must first align.

"Without the political will (by the parties), no mediator could manage to bridge the gaps," said Aaron David Miller, a former U.S. negotiator and public policy scholar at the Wilson Center, a Washington-based think tank. "You could have invited Moses, Muhammad and Jesus and they would not have been able to do it right now."

The Palestinians say Mitchell was ineffective because the Obama administration did not exert the necessary pressure on Israel to maintain — as the United States itself demanded — a construction freeze in Jewish settlements in the West Bank and east Jerusalem, war-won lands the Palestinians want for their state.

Jordan-based analyst Mouin Rabbani said that failure dovetailed with a big credibility problem emanating from the fact that the United States sees itself as a strategic partner of Israel's and therefore is not detached. Still, Rabbani said, while "I wouldn't say that the mediator and identity is irrelevant ... at the end of the day, the mediator is a secondary issue, and I think the Israeli-Palestinian conflict is the perfect example of that."

The former U.S. Senate majority leader was the latest in a long line of mediators to bump up against the Middle East conflict — ranging from diplomats like Dennis Ross to CIA Director George J. Tenet and retired Marine Gen. Anthony Zinni; at times the task was assigned to secretaries of state from William Rogers to Henry Kissinger, George Shultz, Warren Christopher and Colin Powell.

Some enjoyed small degrees of success.

Christopher helped bring Israel and Syria closer to a peace deal in which Israel returned the Golan Heights, captured in 1967 — but it never came about. He helped broker a cease-fire between Israel and the Lebanese militia Hezbollah after an outbreak of fighting in 1996, but what ended the tension there — for a time — was Israel's unilateral pullout from south Lebanon four years later.

Perhaps the most widely attributed successes attributable to U.S. mediation came between Israel and Egypt in the 1970s. Kissinger is widely credited with the separation of forces between the countries in the Sinai Peninsula in 1975, two years after a devastating war; and two years later President Jimmy Carter himself convened Israeli and Egyptian leaders at Camp David for almost two weeks and pushed them into agreeing on a full peace treaty with Israel returning all of the Sinai.

But that was a situation in which the two countries seemed primed for making the move, and the terms of the settlement were relatively simple, and the mediation took the form of direct pressure at the highest level.

"Carter got involved as a mediator only after he was asked by the Israelis and Egyptians," noted Arie Kacowicz, an international relations professor at the Hebrew University of Jerusalem.

The more junior — and full-time — mediators have little to show for their two decades of dealings with Israelis and Palestinians.

Ross helped midwife a series of Israel-PLO interim deals, but only after the breakthrough came in secret talks involving Norwegian and not American middlemen. Ultimately the so-called "Oslo Process" fell apart without Ross, or any other mediator, able to push the sides toward the final settlement that was meant to be reached by 1999 and eludes them still.

Tenet, Zinni and Mitchell spent years on the project with little to show.

Former Israeli Justice Minister Yossi Beilin said Mitchell "failed totally" because the United States resisted presenting a clear outline for resolution.

And even though many say the outlines of a peace settlement are clear, the two sides have never resolved at least two dealbreakers: how to divide Jerusalem — which both want as a capital but where their people are by now significantly intertwined — and how to resolve the Palestinians' demand that millions of refugees and descendants be given rights to return to what is now Israel.

Kacowicz, the Hebrew University professor, said mediators tend to succeed when the sides are ready to do a deal and largely know what it will be. "In a way mediators are most effective when they are less needed," he said. "When the parties are ready to reconcile between themselves, they may need good offices, or some assistance."

Indeed, the Maine Democrat was successful in Northern Ireland in a situation where the two governments overseeing the Belfast talks — Britain and Ireland — agreed years beforehand on the shape of a workable settlement.

Success in that context mainly meant moving the key local parties gradually closer together to the point where they basically settled on what British and Irish governments saw all along as the compromise.

From his arrival in Belfast, all local parties were based in same British government building. Mitchell's shuttle diplomacy involved going from room to room, floor to floor. The deal still took 26 months and required exceptional patience, but Mitchell worked in alliance with two governments and didn't have to persuade them.

In the Middle East, some had hoped the United States would appoint a more interventionist mediator like the late Richard Holbrooke.

And it would seem logical that the nature of the mediator makes a difference: Do they have expert knowledge or familiarity with the antagonists? Are they perceived by all as neutral? Does a track record matter? Is their personality in sync with that of the people they must nudge and cajole?

Some believe it the very doggedness of the mercurial, charming Holbrooke that was key to his success. But history suggests that Holbrooke, too, was successful where the circumstances were already right.

He was for a time considered a mediation magician for his success in brokering the Dayton Agreement of 1995, ending a brutal war in Bosnia that lasted more than three years but also left the two sides impoverished, exhausted, deadlocked and probably aware that they must compromise over the ethnically mixed former Yugoslav republic of Bosnia-Herzegovina.

The same Holbrooke failed utterly to secure peace in the former Serbian province of Kosovo, even though in Serbian president Slobodan Milosevic he had one of the same protagonists as in the Bosnian mediation. The difference: Kosovo's territory was sacrosanct to the Serbs, and the ethnic Albanians of Kosovo were overwhelmingly in the majority and saw an alternative path in which Serbia is simply forced to pull out. NATO eventually attacked Serbia over the issue in 1999 and Kosovo declared independence nine years after that.

In 2005, the Kosovo status issue was handed by the United Nations to former Finnish President Martti Ahtisaari, who won the Nobel Peace Prize several years later for helping douse flames across a broad swath of the world from Namibia to Indonesia. But agreement on Kosovo, with Serbia involved, in the end eluded even him. In 2008, Kosovo declared independence on its own.