Hussein Agha and Ahmad Samih Khalidi have been involved in Palestinian peace negotiations for three decades, and are senior associate members of St. Antony’s College, Oxford, and co-authors of “A Framework for a Palestinian National Security Doctrine.” Agha most recently carried out backchannel negotiations during the Obama Administration’s failed effort to broker an Israeli-Palestinian peace agreement.

As President Trump prepares for yet another attempt to resolve the Palestinian-Israeli conflict, the ground is shifting under his feet. While Israel’s willingness to offer an acceptable deal is increasingly open to question, with nothing to suggest that its terms are likely to soften with time, the Palestinians are sliding toward the unknown. With the slow but sure decay of the Palestinian political scene, the President of the Palestinian Authority, Mahmoud Abbas (Abu Mazen), represents the last slender chance for a negotiated settlement: he is the sole remaining national leader of his people with sufficient, if dwindling, authority to sign and ratify a deal. For President Trump and his team, as well as for all those seeking to end this century-plus-old conflict, there should be no doubt about the moment’s urgency. After Abbas, there will be no other truly weighty representative and legitimate Palestinian leadership, and no coherent national movement to sustain it for a long time to come.

Over six days in late November and early December, 2016, Fatah, the Palestinian national liberation movement, convened its seventh congress in Ramallah, the de-facto capital of the Palestinian Authority. Despite the lengthy speeches and festive air, the conference did little to dispel what had become unmistakable: the slow expiry of a once vibrant movement. Long on show and short on substance, the meeting hardly touched on any of the mounting political challenges facing the Palestinian people. The Congress was no more than a confirmation of the current order and a reaffirmation of its total and unprecedented control over Fatah, the P.A., and its ostensible parent, the Palestine Liberation Organization.

The contemporary Palestinian national movement—founded and led by Yasser Arafat and embodied by the P.A., Fatah, and the P.L.O. over the past half century—is reaching its end. As its institutions wither and its leaders fade away, there is no obvious successor to take its place.

Looking back, the 1993 Oslo Accords marked the Palestinian national movement’s highest political accomplishment and the beginning of its slow decline. From then onward, the P.A. has been trapped between its original revolutionary mission as an agent for liberation and its new responsibilities as a proto-state, with its attendant civil, bureaucratic, and security establishments.

For a while, with its historic resistance leader at the helm, the national movement sought to reconcile its contradictory missions. But, with Arafat’s death, Fatah lost not only the forefather and leader of its foundational militant phase but its very raison d’être. Without “armed struggle,” the national movement had no clear ideology, no specific discourse, no distinctive experience or character. In the absence of a genuine and independent state, it was unable to transform itself into a ruling party, as, for example, the African National Congress did, in South Africa. It remained incomplete and suspended: a liberation movement not doing much liberating, locked in a fruitless negotiating process, and denied the means of government by a combination of Israeli obduracy and its own inadequacies.

With the passing of Arafat and most of his colleagues, Fatah’s ability to hold its fractured parts together waned. The social and political milieu of the West Bank and Gaza—steeped in clannish and personal influences—highlighted local fiefdoms and deep-rooted tensions. Severed from its history in the lands of exile, and without a rationale to supersede its original liberationist impulse, Fatah became mired in narrow and parochial turf wars. This was, in turn, compounded by its leaders’ failure to attract new blood. Unlike the experience of exile that formed a unifying Palestinian bond, that of the territories never managed to produce viable leaders who could forge a truly national enterprise out of highly localized components. The powerful pull of local ties made it almost impossible for a Hebronite to have a genuine popular base in Ramallah, or for a Gazan to have a credible say in the West Bank.

With no new leaders, no convincing evidence of validation, no marked success in government, no progress toward peace, fragile links to its original setting abroad, and a local environment buffeted by the crosswinds of petty quarrels and regional antagonisms, Fatah fundamentally disappeared as a real political agent.

The national movement was built on representation, activism, and achievement. It faithfully and energetically represented the broadest spectrum of Palestinian national sentiment, from the most visceral to the most rational, and it re-created the forgotten Palestinians as central players in their own drama and as a cause worthy of recognition across the world—epitomized by Arafat’s address to the U.N. General Assembly in 1974.

Today, none of these elements of success are evident. The all-encompassing P.L.O. has lost its representative status; the aging factions that still sit in its councils have little, if any, extensions inside or outside Palestine. The spirit of activism and dynamism has moved outside P.L.O. structures and onto the streets with no clear organization or political direction. And the P.A./P.L.O.’s achievements have been largely formalistic if not fake—a more advanced status as “observer state” at the U.N., but with no tangible improvement to the situation on the ground.

Arafat’s management was an integral element of the dynamism of the Palestinian national movement, and the transition from Arafat to Abbas passed smoothly because it was recognized as a continuation of the founding days of the national movement. Abbas may have needed formal elections to consolidate his position and gain acceptance in the international community, but, without his previous revolutionary credentials and association with Arafat, Abbas’s legitimacy would have been questioned from the start.

Abbas did not want, and could never occupy, Arafat’s place. His standing with his own people was deeply damaged by his persistent and infertile engagement with the peace process, his unwavering opposition to forceful struggle, and his fulsome dedication to security coöperation with Israel. As his tenure extended beyond his initial electoral mandate, the Palestinian political system developed many of the characteristics of a one-man Presidential regime, but without the élan of a popular leader. Later years witnessed a growing tendency toward unmitigated centralization, rule by decree, and the concentration of power. Other instruments of government were muted, and a determined effort was made to control what remains of Fatah’s decaying structures and to silence genuine political dissent. What used to be a vibrant if fractious political debate, nourished, tolerated, and often exploited by the leadership, has turned into a dull and dismal discourse, steered by political directives, and driven by fear of suppression and the loss of position inside an ever-swelling bureaucracy. A distinction between “President” and “leader” has emerged, and not necessarily in a manner that serves either.

Abbas’s years as President have not been without their share of achievements. His peace policy provided the P.A. with a formidable firewall against the kind of international pressure associated with the Palestinian national movement’s past violence, and added to a growing sense of unease at Israel’s occupation. For some, this by itself is a major national achievement. The P.A. has been sustained as a would-be state, and, since 1994, many of the day-to-day governing affairs of municipal, health, education, and other functions have been in Palestinian hands for the first time.

Abbas’s dedication to negotiations, diplomacy, and non-violence has shifted the burden onto the other side. While the current Israeli leadership’s peace credentials are widely disputed, Abbas’s international image as a man of peace remains largely intact. At the same time, he has managed to hold on to the historical and fundamental Palestinian demands; he has not wavered from the P.L.O.’s goals for a state along the 1967 borders, with its capital in East Jerusalem, and a just resolution to the refugee problem. He put an end to the chaos of the second intifada. He has continued engaging with a broad range of Israeli opinions, and has assiduously sought to cultivate what remains of the Israeli peace camp and to engage with Jewish leaders and communities abroad. Perhaps most important, he has succeeded in insulating the Palestinian people from much of the violence and destruction of the “Arab Spring” and from the growth of Salafi and jihadist movements in the West Bank.