THE HAMAS movement handed control over border posts in the Gaza Strip on Wednesday to the Palestinian Authority, the first step in implementing a reconciliation agreement between the rival factions. The deal demands a healthy dose of skepticism: Half a dozen previous unification pacts between the two movements have broken down since their violent split a decade ago, and the most difficult questions about this one have yet to be tackled. Still, the border handover promises a measure of humanitarian relief to Gaza's long-suffering population, which is something that both Israel and the United States ought to welcome.

Conditions for the nearly 2 million people packed into Gaza, which is about twice the size of the District of Columbia, have deteriorated considerably this year. Egypt, concerned about links between militants in Gaza and an Islamic State affiliate in the Sinai Peninsula, has kept the border sealed, and Palestinian Authority leader Mahmoud Abbas compounded the hardship by drastically reducing funding and electricity supplies. Hamas's response, brokered by Egypt, has been to offer to turn the civilian government of the territory over to the Palestinian Authority, beginning with the border crossings. That should allow the restoration of basic services and an increased flow of goods.

The problem is that Hamas's leadership appears more wedded than ever to its determination to "erase Israel from the map," as its political chief in Gaza recently put it, and it has rejected the disarmament or disbanding of its 20,000-plus-member militia, which wields an arsenal of rockets and has fought three wars with Israel since 2008. Mr. Abbas has declared that ministers in a new coalition government the two sides may negotiate would have to recognize Israel and that Hamas would not be allowed to maintain an armed force not answerable to that government. But he lacks the means to enforce either condition.

If Hamas is included in a new administration, the Palestinian Authority would risk losing the $400 million a year in funding it receives from the United States, and Israel has said any such coalition is unacceptable. That probably means that if the Palestinian rapprochement continues, it would do so with fudges meant to paper over Hamas's continued militancy. At best, that might allow humanitarian relief for Gazans and lower the risk of a new war with Israel. At worst, it could discredit and eventually destroy Mr. Abbas's administration, which for a decade has kept the West Bank mostly peaceful through close security cooperation with Israel.

The Trump administration, which purports to be working on a Mideast peace plan, has taken a cautious interest in the ongoing negotiations between the Palestinian factions, rightly insisting that Hamas disarm and recognize Israel before it joins a unity government. Were that to happen, there might be a genuine opening for a peace process. More likely, the United States and Israel would find themselves treading a fine line between encouraging better living conditions in Gaza and preventing Hamas from shedding the burdens of governing while continuing to seek Israel's destruction.