The U.S. issued a threat to Venezuela. Now, it has to follow through.

The deadline has come and gone. Venezuelan President Nicolás Maduro took some half-steps toward election reform on Nov. 30 that hardly fulfill Mr. Blinken’s conditions. The State Department called the half-steps an “important development” but said it was “deeply concerned by the lack of progress” on prisoner releases.

What’s at stake is the credibility of the United States. If the secretary of state vows to take specific action by a specific date, and then does not, the world will notice and assume the United States is not serious. Mr. Maduro undoubtedly will draw the same conclusion, that he can pocket the gains of sanctions relief while not paying the price demanded by Mr. Blinken, and no one will do anything about it. Mr. Blinken ought not remain silent.

The United States lifted some sanctions on oil and gold exports in October after the Maduro government and the Venezuelan opposition, known as the Unitary Platform, signed an agreement in Barbados setting out a road map to free and fair elections next year. The deal stipulated that Mr. Maduro would allow international observers and provide all candidates freedom of movement and assembly as well as equal access to the media. A key test is the candidacy of María Corina Machado, a conservative former legislator who was picked in an informal primary to lead the opposition. She is viewed by many voters as having the best chance to oust Mr. Maduro but was barred from running in June by Mr. Maduro’s government, based on charges that she failed to complete a declaration of assets and income when she was a legislator.

On Nov. 30, facing the deadline to start complying with the Barbados agreement, Mr. Maduro and the Unitary Platform issued a statement saying they had agreed that all candidates who are barred from running can appeal their bans to the nation’s highest tribunal. The appeals must be filed by Dec. 15. This is hardly a major concession, because the court is basically an arm of the Maduro regime, and as recently as Oct. 31 issued a decision suspending the primary that elected Ms. Machado.

Mr. Maduro is doing the very minimum. Mr. Blinken’s demand was for Venezuela to “define a specific timeline and process for the expedited reinstatement of all candidates. All who want to run for President should be allowed the opportunity, and are entitled to a level electoral playing field, to freedom of movement, and to assurances for their physical safety.” At the very least, Mr. Maduro must allow Ms. Machado to run.

Mr. Maduro has taken no known action to meet Mr. Blinken’s other demand to “begin the release of all wrongfully detained U.S. nationals and Venezuelan political prisoners.” Three U.S. citizens are still wrongfully detained in Venezuela: Eyvin Hernandez, Jerrel Kenemore and Joseph Ryan Cristella. The families of all three have denied the prisoners were involved in any wrongdoing.

“Failure to abide by the terms of this arrangement will lead the United States to reverse steps we have taken,” Mr. Blinken insisted.

To preserve his credibility and that of the United States, Mr. Blinken needs to respond with sanctions that squeeze Mr. Maduro and his gang, who have driven Venezuela to ruin. Who else in the hemisphere will take seriously the U.S. call to stand up for democracy if the Venezuelan dictator gets off the hook so easily and can now bank billions of dollars in new oil revenue?

President Biden does not want a dispute with Mr. Maduro now, while the rest of the world is feeling the instability caused by two wars. And Mr. Biden no doubt wants to see lower gas prices going into an election year. Mr. Maduro, who falsified earlier balloting, might think he can hold on to office next year, but he is also taking pains to minimize the chances he could lose. Apart from his ban on Ms. Machado’s candidacy, his government held a strange weekend referendum in which voters approved taking over a sizable portion of neighboring Guyana — an effort to rally support for the government before the election.

Mr. Maduro’s behavior might have been predictable. But that does not make it any more acceptable.