Venezuela’s Maduro is breaking through all red lines. Time to respond.

The United States lifted some sanctions in October after the Maduro government and the Venezuelan opposition, known as the Unitary Platform, agreed in Barbados on a “road map” that would lead to elections. It stipulated that all candidates would enjoy freedom of movement and assembly, that each party could select its own candidates and that they would have equal access to the media.

But Mr. Maduro has contemptuously violated the agreement. In June, the regime barred María Corina Machado, the most popular opposition leader, from running, based on specious corruption allegations. Ms. Machado overwhelmingly won an unofficial opposition nominating contest. She appealed the ban, but on Jan. 26, the Maduro-controlled Supreme Court turned down her bid for reinstatement.

Not giving up, Ms. Machado on March 22 designated a stand-in candidate, Carina Yoris Villasana, a little-known 80-year-old philosophy professor, widow and grandmother. As the deadline for registration of candidates came on March 25, the opposition was unable to log in to the electoral council’s online system to sign Ms. Yoris up. “We’ve exhausted all of the possibilities,” Ms. Yoris said at a news conference. “It’s not just the name of Corina Yoris that is being denied but the name of any citizen that wants to run.” After this, a party in the opposition coalition was granted an extension and logged into the system to register Edmundo González Urrutia, a former ambassador. The opposition said the choice was “provisional ... given the clear impossibility of registering the chosen candidate so far.” The parties can make changes on their ticket until mid-April; it is possible a new opposition candidate will be named. The timing will be critical, because the U.S. decision on sanctions has to be made by April 18. So far, 10 candidates have registered, but none are connected to the opposition coalition, and some have ties to Mr. Maduro or lack plausible chances to win. Polls show that the president is hugely unpopular and that Ms. Machado would defeat him if she could run.

To make matters worse, Mr. Maduro’s security apparatus has attempted to silence Ms. Machado’s core of advisers. Two of them, Dignora Hernández and Henry Alviarez, were seized in recent days and have not been heard from, her staff says. Several others, including Ms. Machado’s campaign manager, facing arrest warrants, have taken refuge in the Argentine Embassy. David Smolansky, Ms. Machado’s representative in Washington, told us she is physically endangered. “Her life and freedom are at risk,” he said.

More than 7.7 million Venezuelans have fled the country, a tide that increased in the mid-2010s as the country’s economy nosedived. Venezuelans now make up the second-largest number of migrants at the U.S. southern border, after Mexicans. Mr. Maduro has turned to U.S. adversaries Russia, Cuba and Iran for security, military and economic help. Usually cautious about criticizing the socialist Maduro, the leftist leaders of Colombia and Brazil have expressed unease about his authoritarian trajectory.

Mr. Blinken demanded on Oct. 18 that Mr. Maduro “define a specific timeline and process for the expedited reinstatement of all candidates.” He added, “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.” He also said, “Failure to abide by the terms of this arrangement will lead the United States to reverse steps we have taken.”

Though probably worth trying, the Biden administration’s gamble — lifting sanctions in a bid to prompt democratic progress — has thus far failed, abjectly. The credibility of the United States is at stake in the response. The administration could reimpose the oil sanctions that existed before, in whole or in part, or seek equivalent measures to pressure Mr. Maduro. The Venezuelan leader has, like President Vladimir Putin of Russia, managed to survive sanctions, buoyed by an economy that runs on illicit flows of cash from drug trafficking, mining and smuggling. The United States needs to be smarter with sanctions and seek more cooperation from Europe and other Latin American nations to help isolate Mr. Maduro’s regime. Otherwise, Mr. Maduro will continue to destroy what was once among the wealthiest and most democratic nations in Latin America.