I VÁN DUQUE won Colombia’s presidency last year on a promise to modify a peace deal between the government and the FARC guerrilla group, which ended their 52-year war in 2016. On March 10th this year Mr Duque kept that promise. In a televised speech he stated six objections to a law governing the operation of a tribunal, known as the JEP , that investigates and judges members of the FARC and the armed forces for war crimes and crimes against humanity. Although congress passed the law in 2017 and the constitutional court endorsed it, Mr Duque is sending it back to the legislature. “We want a peace that genuinely guarantees truth, justice, reparation and non-repetition,” he said. But his decision is a blow to the peace process.

This is the first time a Colombian president has reopened a legal question that had been settled by the constitutional court. It is not clear that congress has the power to change such a law for the reasons Mr Duque put forward, or that it will do so.

During his seven months in office, Mr Duque has tried to strike a balance between the hard line of his mentor, Álvaro Uribe, a former president who opposes the peace accord, and Colombians who want to preserve it. Now he seems to have backed Mr Uribe’s policy. The president wants former FARC members from lower ranks to go on trial and to ensure that the FARC compensate victims with their own assets.

This may be smart politics. The JEP , which can issue lenient sentences to ex-fighters who confess to their crimes, is unpopular. It became more so on March 1st when the attorney-general’s office arrested a JEP prosecutor for allegedly taking a $500,000 bribe to protect a former FARC commander from extradition to the United States. Bashing the tribunal is a way for Mr Duque to boost his own popularity, which plunged last year after he proposed an increase in value-added tax, though it has since recovered.

The success of his gambit now depends on congress and the constitutional court. Congress could override Mr Duque’s objections, forcing him to sign the law. That would be a humiliation. Even if congress passes a modified law, the constitutional court is likely to strike it down. That would be a better result for Mr Duque. The court would take up to a year to rule.

In the meantime, the JEP will continue to function, but clumsily. Without the guidelines set out in the law, which give priority to trials of the most important FARC leaders or army officers, it will be up to six of the tribunal’s judges to decide which defendants to try first. The danger is that the tribunal will start more trials than it can complete within its ten-year mandate. An overburdened JEP might end up convicting and punishing no one.