Lawmakers in Washington and around the country are in an uproar over what they derisively call “sanctuary cities.” These are jurisdictions that limit cooperation with federal immigration enforcement, or try in other ways to protect unauthorized immigrants from unjust deportation.

The Senate is voting Tuesday on a bill from David Vitter of Louisiana to punish these cities by denying them federal law-enforcement funds. The House passed its version in July. North Carolina’s Legislature has passed a bill forbidding sanctuary policies. Lawmakers in Michigan and Texas are seeking similar laws.

These laws are a false fix for a concocted problem. They are based on the lie, now infecting the Republican presidential campaign, that all unauthorized immigrants are dangerous criminals who must be subdued by extraordinary means.

The laws are a class-action slander against an immigrant population that has been scapegoated for the crimes of a few, and left stranded by the failure of legislative reform that would open a path for them to live fully within the law. And because crackdowns on sanctuary cities seek to thwart sound law-enforcement policies and the integration of immigrants, they are an invitation to more crime and mayhem, not less.