President Biden on Saturday suggested he might cut off US military assistance to Israel if it moved forward with a military operation to dismantle Hamas’ last stronghold in the Gazan city of Rafah. An Israeli victory over Hamas is now a red line for a president surrendering to a pro-Hamas political base. Americans should understand the consequences of that red line: A guarantee that Oct. 7 will happen again, that hostages will never come home, that an emboldened Iran will escalate on all fronts and that Hamas-oppressed civilians will suffer indefinitely. After dismantling Hamas’ operational control over northern and central...