When the political party representing El Salvador's former Soviet-backed guerrillas won the presidency in 2009, some of its opponents took comfort in the separation of powers dictated by the Salvadoran constitution. Despite the Marxist roots of the Farabundo Martí National Liberation Front (FMLN), and the uncertainty about what it might do with its new power, there was an independent judiciary obliged to uphold the rule of law.

But in a private conversation in San Salvador around that time, one seasoned member of the center-right Arena party confided in me his fears that the FMLN would not be able to keep its hands off the Supreme Court.

Now it's clear that he was right. And the international community that was so indignant about the lawful, strictly constitutional removal of Paraguay's President Fernando Lugo has uttered nary a peep of objection to what amounts to a blatant attempt by the FMLN to crush the democratic order in El Salvador.

If the country is to be spared a consolidation of power similar to what has occurred in Venezuela, Nicaragua, Ecuador and Bolivia, protests from civil society and politicians of every stripe who care about democracy are its only hope.

El Salvador was once considered among the most promising Latin American market economies. But all that came to an end with the 2004 election of Antonio Saca, the fourth consecutive Arena president. Mr. Saca was nothing like his reform-minded predecessors. He behaved more like a Chicago ward politician, and his party, which was by then drunk with power, let him get away with it. His tenure was marked by declining economic competitiveness and a rising number of corruption scandals.

In the 2009 presidential election, FMLN candidate Mauricio Funes, a television journalist, successfully offered himself to voters as a moderate leftist and a healthy alternative for Salvadorans suffering Arena fatigue. Unfortunately, President Funes brought the rest of his party to power as well, and many of them remain card-carrying extremists.

Vice President Salvador Sánchez Cerén, a former guerrilla "comandante," is a classic example. He has never managed to tame his lust for power or his hatred for a free society. When Islamic terrorists toppled the World Trade Center on 9/11, he led celebrations and American flag burnings in the streets of San Salvador.

Now Mr. Sánchez Cerén is the FMLN candidate for the 2014 presidential election, and the party is engaged in a showdown with the high court. This is not a coincidence.

The constitutional panel of the high court butted heads with the FMLN by ruling against the unlawful elections of 10 Supreme Court magistrates by the national assembly in both 2006 and 2012. Its decision does not discriminate politically. The 2006 violation occurred under an Arena-controlled assembly, and the 2012 violation occurred under an FMLN-controlled assembly.

But the FMLN is furious and, remarkably, has appealed the decision to the multilateral body known as the Central American Court of Justice. Obviously this court has no jurisdiction over the Salvadoran Supreme Court. But it is made up of friends of the FMLN, including judges controlled by Nicaragua's Sandinistas, and is therefore a convenient panel of "experts." Granting it power over El Salvador's high court flouts constitutional order.

This is precisely what the FMLN intends. If the Central American court rules against the Salvadoran high court, and the outside ruling is allowed to stand in El Salvador, it would establish a precedent that gives the legislative body power over the Supreme Court. The national assembly could then shape the court according to its own political agenda and destroy its independence.

Writing on the website elsalvador.com, economist and highly respected Salvadoran intellectual Manuel Hinds explained one practical, short-term benefit of the power grab for the FMLN party bosses. It has to do with a recent court ruling that ends the electoral practice of voting for party lists in legislative elections and instead mandates that voters must be allowed to vote for individuals.

"The vote for a person erodes the power of the leadership that always decided not only who would be the candidate but in what order they would be elected," Mr. Hinds pointed out. The long-run goal, he explained, is to "allow the [party] leadership to violate the constitution repeatedly with the support of the constitutional high court."

All is not yet lost. Civil society is in an uproar against the attempt to destroy the court, and the pushback cuts across the ideological spectrum.

But it is not enough. As Mr. Hinds points out, the country needs "a political mobilization" by party members on both sides who care about democracy and are willing to confront "tyranny, corruption and lies." Both sides, he notes, were able to reach the peace accords after the civil war, so it's been done before. The survival of Salvadoran democracy depends on it.

*O'Grady@wsj.com