Flickr/SecDef.Early in his tenure as Israel’s foreign minister, Avigdor Lieberman explained why he refrained from heading diplomatic negotiations with the United States over the Palestinian issue: “For me to deal with this issue – it would be a clear conflict of interest,” he said, alluding to the fact that he lives in a settlement in the West Bank. “I wouldn’t want to be accused of intentionally sabotaging the negotiations.”

The Israeli government’s solution to the problem—to the fact that Israel’s top diplomat had a “conflict of interest” on a core foreign-policy issue—was to send Defense Minister Ehud Barak in Lieberman’s stead. Barak, as head of the dovish Labor party, served as prime minister between 1999 and 2001 and maintains longstanding working relationships in Washington and elsewhere. In the current and generally-hawkish government of Prime Minister Benjamin Netanyahu, Barak functioned as one of Israel’s de-facto foreign ministers, as did, to a lesser degree, President Shimon Peres. He offered, as some suggested, diplomatic cover for Netanyahu’s right wing coalition and served as an interlocutor between Netanyahu and the U.S. administration.

This kind of arrangement will likely not be available to the next Israeli government, to be formed in early 2013. Barak, facing electoral defeat, retired this week from political life, citing a desire to spend more time with his family. The next prime minister (Netanyahu or his successor) could still appoint Barak as a minister in a future cabinet, as some have suggested (see here as well), but this would require determination and considerable political will on the part of the Prime Minister. More likely than not, Barak will leave the defense ministry—and his diplomatic role—with the formation of a new government.

Barak’s retirement stems from a paradox: though he is one of Israel’s most influential strategists and practitioners, having shaped much of its recent foreign policy, he is deeply unpopular with the public. He is—by all accounts—analytically brilliant, yet plagued by mistrust and even dislike from many of his peers. As Prime Minister he alienated many of his senior ministers and left his voters, many of whom were jubilant at his election, disillusioned and disappointed. He remains, many believe, a commando officer at heart: brilliantly executing complex (at times overly complex) plans but incapable of collaborating effectively with anyone.

To many on the right—including many in the current coalition—he remains the Labor leader who offered a far reaching proposal to Palestinian leader Yasser Arafat. To some people’s shock, he negotiated over the division of Jerusalem as a capital of both Israel and Palestine. To many on the left, he remains the man most responsible—besides Arafat—for anchoring the perception in Israel that there is no partner for peace on the Palestinian side; he presided over the long-term electoral calamity that befell the Israeli left wing in the aftermath of the Camp David summit of 2000 and the subsequent outbreak of the Second Intifada.

An exception to the Barak-the-brilliant-loner rule, for a while, was his collaboration with Prime Minister Benjamin Netanyahu in the current cabinet. Barak and Netanyahu have known each other for decades; Barak was Netanyahu's commander in the Israeli elite unit Sayeret Matkal in the early 1970s, and later unseated and succeeded him as prime minister in 1999. To the surprise of many, Barak proved able to work harmoniously as defense minister under Netanyahul’s leadership. Most notably, they alone seemed to share the full extent of Israel’s planning with regard to Iran’s nuclear program. Barak was often the voice of the Netanyahu-Barak duo on Iran, in interviews abroad and background briefings.

Barak’s departure, if it is indeed final (never a given in Israeli politics,) will have considerable effect on Israel’s foreign policy. On Iran, it removes a leading hawk from the country’s innermost decision-making circles. On the Palestinian front, it removes one of the few remaining ministers who still urge a proactive Israeli approach. And in Washington and other foreign capitals, it will remove one of Israel’s main de facto foreign ministers.

Natan B. Sachs is a Fellow at the Saban Center for Middle East Policy at the Brookings Institution. He is currently writing a book on the domestic political underpinnings of Israel’s foreign policy. Follow him on twitter: @natansachs.