Mr. President,Earlier this week, 73 members of your party in Congress publicly urged you to reverse your predecessor’s policies toward Palestine. It seems like they won’t need to exert much effort to convince you, as earlier this year your administration allocated $235 million to the Palestinians, presented as part of an effort to “restore credible engagement” in the world’s most bitter conflict.But I am here, sir, with a painful reminder: No American engagement in Israel and the Palestinian territories would ever be credible until my son comes back home.Here, in case you need it, is the story: Early on August 1, 2014, at the tail end of yet another round of bloodshed provoked by Hamas, a ceasefire finally took hold. It was brokered by the United Nations and the Obama administration. Two hours later, it was blatantly violated when Palestinian terrorists, taking advantage of the lull in fighting, used one of their tunnels to creep into Israel. They shot and killed two soldiers, and abducted another—my son, Lieutenant Hadar Goldin.Hadar was almost certainly killed in action, and we demanded that his body be returned to us for proper burial. John Kerry, then secretary of state for the administration in which you also served, agreed. “The United States condemns in the strongest possible terms today’s attack,” he said in a statement. “It was an outrageous violation of the ceasefire negotiated over the past several days, and of the assurances given to the United States and the United Nations. Hamas, which has security control over the Gaza Strip, must immediately and unconditionally release the missing Israeli soldier, and I call on those with influence over Hamas to reinforce this message.”You, Mr. President, now have influence over Hamas. You can, and must, demand that Gaza’s rehabilitation be contingent upon the return of my son and of Oron Shaul, another Israeli soldier whose body is held captive by the terrorist organization.Sadly, while diplomats—including your new ambassador to the U.N., Linda Thomas-Greenfield—continue to affirm the validity of our case, no concrete pressure has yet been exerted on Hamas or its paymasters in Iran. This week, the organization continued to restore its capabilities, propping up some of the power stations damaged during its recent assault on Israel. When asked if the organization was indirectly enjoying U.S. aid, a State Department spokesman last week said it was possible.“We’re going to be working in partnership with the United Nations and the Palestinian Authority to kind of channel aid there in a manner that does its best to go to the people of Gaza,” the unnamed official told the press while previewing Secretary of State Antony Blinken’s visit to the region. “As we’ve seen in life, as we all know in life, there are no guarantees.”But a guarantee, Mr. President, is precisely what we need right now: not just to me, a mother, awaiting her son’s return, but to Israel at large and, for that matter, to any nation that wonders whether it should take this new administration at its word. Unless this agreement—for which you, as President Obama’s second-in-command, have a measure of responsibility—is honored and implemented, there’s no reason to believe that American diplomacy and American might are more than just a host of empty promises.Instead, I hope you instruct your senior officials to implement one simple principle: Not another dime to any Palestinian organization until Hadar is brought back for burial in Israel, and not another day of negotiations with anyone—be they in Tehran or Qatar—who has any influence on the fanatics in Gaza and fails to insist on our son’s return. This is not just a sound and elementary negotiations technique—making sure promises are honored—but also a human rights issue, the humans in question being my son and our family, which deserves the same basic dignity we wish for people everywhere.Stand up to your promise, and you’ll win the approval of your party as well. As you may recall, a host of prominent Democrats—including Keith Ellison, arguably the most prominent Muslim in American politics and the former deputy chair of the Democratic National Committee—have joined us throughout the years in demanding that Hamas honor its promise to America. They did so because they realized that Hadar was the victim of an American-brokered ceasefire, and because they, like any decent person, were outraged by the intolerable cruelty of denying my son his final resting place.So as you continue to chart America’s course in the Middle East, contemplating dramatic overhauls and pushing for fresh starts, you could do no better than begin with one immense, long-overdue confidence-building measure: Bring Hadar back home.