After 16 months of fruitless negotiations with Democrats in Congress, President Bush sent the U.S.-Colombia Free-Trade Agreement to Capitol Hill this week. Under existing rules, lawmakers have 90 days to vote on the legislation. But Nancy Pelosi intends to hold a vote today that would change the rules, allowing Democrats to quietly kill the bill.

Such a maneuver would signal that protectionism has made a comeback in Washington, meaning fewer opportunities for American businesses and higher prices for American consumers. Rejecting the deal would also undercut a valuable ally in a region where the U.S. needs all the friends it can get.

U.S. markets already are wide open to Colombian goods. The U.S. long ago removed barriers to Colombian exports, products that range from coffee to essential industrial materials such as nickel, copper, coal, and oil. More than 90 percent of Colombian goods already enter the U.S. duty-free under the terms of the Andean Trade Preferences Act, which Congress reauthorized with overwhelming support less than two months ago.

By contrast, during the 16 months in which Congress has delayed passage of the Colombia free-trade agreement, American exporters have paid more than $1 billion in tariffs on exports to Colombia. The free-trade agreement would remove those tariffs and give American businesses the same access to Colombia’s markets that Colombian businesses have to ours.

Diplomatically, the deal would strengthen our economic and security ties to a country that shares our interest in countering terrorism and authoritarianism in South America. Colombian President Alvaro Uribe has courageously confronted Hugo Chavez and his thuggish allies in the region over their support for the narco-terrorists responsible for much of the violence in his country. Uribe deserves our support, and a trade accord would bolster his administration while benefiting both our nations’ economies.

Democrats in Congress initially objected to the deal on the grounds that it did not include sufficient protections for Colombian workers and the environment. Since then, the Bush and Uribe administrations have made extraordinary concessions to address these concerns. Last year, they amended the agreement to include nearly every new labor and environmental standard Democrats demanded. A similar compromise cleared the way for the passage of a free-trade agreement with Peru last December.

The Colombia free-trade agreement includes the same standards as the Peru deal, but we’re now deeper into an election year in which the Democratic candidates for president have decided that denouncing trade works to their advantage in Ohio and Pennsylvania. Most recently, Hillary Clinton demoted top adviser Mark Penn for working to pass the agreement in his capacity as chief executive of a public-relations firm.

This situation has congressional Democrats in a bind. The substantial case for passing this particular deal is rock solid. It imposes no costs on the U.S. economy. It would strengthen diplomatic ties to a key ally in a vital region. It includes enforceable protections for workers and the environment. It is practically identical to an agreement with Peru that Congress just passed. But with the party’s presidential contenders (and the union bosses who own them) increasingly committed to opposing any free-trade agreement, congressional Democrats are falling in line. Now they say that they can’t support the deal until Colombia shows “sustained progress” in addressing violence against labor unionists.

A recent Cato Institute study shows that this complaint does not withstand much scrutiny. Between 2002 and 2007, the number of unionists killed fell by 88 percent. If such an advance cannot convince the Democrats that Colombia has made “sustained progress” in curbing the violence against labor activists, then nothing can.

Political violence in Colombia is not reserved for union leaders. Decades of civil war have made violence an issue for all Colombians. President Uribe has done an admirable job protecting vulnerable groups, including labor organizers. But if he is to continue his good work, he needs more cooperation from the United States, not less. Without a free-trade agreement with the U.S., Colombia is put at an economic disadvantage against neighboring countries such as Peru, which has a trade deal. That’s no way to treat an ally. Hurting the Colombian economy won’t help Uribe to quell the violence in his country. If anything, it will make the violence worse.

As it stands, Colombia is our closest ally in Latin America. President Uribe’s embrace of free markets stands in stark contrast to the socialist authoritarianism Hugo Chavez is trying to spread throughout the region. We should be rewarding such an ally, not punishing him. If congressional Democrats vote to kill the U.S.-Colombia Free-Trade Agreement, they will be weakening both the U.S. economy and Uribe — while doing Chavez a huge favor in the process.