Recent weeks have not been kind to the Grand Old Party. Republicans have been embarrassed by Donald Trump’s racist attacks on Gonzalo Curiel, the federal judge presiding over a fraud lawsuit against Trump University. They have watched him assault popular GOP leaders like Speaker Paul Ryan and New Mexico Gov. Susana Martinez. Many among the party faithful are realizing that Mr. Trump may flame out before Election Day—and that he could bring the party’s slate of candidates down with him.

Yet conventional wisdom remains that Mr. Trump’s nomination is inevitable. The theory is twofold: First, his primary victories give him enough delegates to prevail on the first ballot at the Republican convention in July. Second, those delegates are bound to vote for Mr. Trump by state laws and GOP rules.

Not so fast. Although 20 states have passed laws that purport to bind delegates, these statutes can’t be legally enforced. When Republican delegates arrive in Cleveland to select their party’s nominee, they should recognize that they are bound only by their consciences.

It’s true that Rule 16 of the Republican National Committee says primaries will be used to “allocate and bind” delegates. But that rule expires at the convention’s start. Though a majority of delegates could vote to adopt a binding rule at the convention, that’s unlikely. It has happened only once before, in 1976, when loyalists of President Ford sought to block the insurgency of Ronald Reagan. This year the Rules Committee will be packed with supporters of Sen. Ted Cruz, who has not endorsed Mr. Trump.

State laws that purport to bind delegates can’t be enforced without violating the First Amendment. A political party is a private association whose members join together to further their shared beliefs through electoral politics, and they have a right to choose their representatives. The government has no business telling parties how to select their candidates or leaders: That would be a serious infringement of the rights to free association and speech.