For months, the Biden administration has been pursuing an ambitious diplomatic project to design a new Middle East for a new era. But the old Middle East, it turns out, still has something to say about it.

The stunning Hamas assault on Israel on Saturday served as a gut-wrenching reminder that the decadesold conflict with Palestinians remains a cancer that has not gone away even as leaders in Washington, Jerusalem, Riyadh and other Arab capitals would prefer to focus on building a revamped region.

U.S. officials said it was too early to say whether the attack was explicitly motivated by a desire by Hamas or its patron Iran to disrupt President Joe Biden’s effort to broker a landmark deal between Israel and Saudi Arabia that would profoundly reorient the Middle East. But they acknowledged that it could complicate the already delicate negotiations and make it that much harder to reach an agreement akin to the Abraham Accords between Israel and smaller Arab nations.