Colombian President Juan Manuel Santos speaks about the current situation in Colombia at the Wilson Center in Washington on Feb. 2. (Saul Loeb/AFP/Getty Images)

On a hot, steamy evening 15 years ago, Bill Clinton donned a sombrero, ignored his nervous presidential security detail and joyfully danced his way through cheering crowds in the 16th-
century central plaza of Cartagena, Colombia’s graceful Caribbean city.

Leading a congressional delegation that included the Republican House speaker, J. Dennis Hastert, and Joe Biden, then the senior Democrat on the Senate Foreign Relations Committee, Clinton had just formalized a deal to provide Colombia with $1.3 billion in aid. It was the first contribution to what was to be a major effort to stop the massive flow of Colombian cocaine into the United States.

Three administrations and $10 billion later, what is known as “Plan Colombia” is widely considered one of the most successful U.S. assistance efforts in history. As it morphed into a counter­terrorism program — and came to include democracy development and trade deals — it is one of the few major foreign policy initiatives in decades that has maintained strong bipartisan support.

Today, Colombia is on the verge of signing a historic peace deal with leftist guerrillas that will end a half-century of internal war. Despite the falling price of oil, its biggest export, the Colombian economy is one of the most robust in Latin America, and the country is a prime destination for U.S. and global investors. Once on the verge of becoming a failed state, it has made significant strides on virtually every development indicator.

The only thing that hasn’t changed is Colombia’s position as the world’s No. 1 exporter of cocaine. After dipping down for several years, both cultivation of coca, the raw material of cocaine, and production of the drug have seen sharp in­creases in the past three years.

Drug trafficking is on the agenda Thursday when President Obama meets at the White House with Colombian President Juan Manuel Santos. But for the most part, the visit will largely be one of celebration, marking the 15th anniversary of Plan Colombia.

For Obama, it is an addition to his list of recent foreign policy triumphs, along with the Iran nuclear deal, trade promotion agreements and the diplomatic opening to Cuba, as he nears the end of his presidency. Although he didn’t start it, Obama has nurtured the program and pushed for its continuance.

Santos, in remarks Wednesday, said, “I’ve come here to say thank you, to the American people, to the American government,” for helping Colombia “go through a difficult time.” And, he noted, to ask for more help to consolidate gains and secure the upcoming peace.

The White House said this week that its fiscal 2017 budget request will include an increase for Colombia over about $300 million this year. “This request will demonstrate our intention to help Colombia successfully implement its peace agreement,” said Mark Feierstein, National Security Council senior director for Western Hemisphere affairs.

Although U.S. officials declined to provide a figure, Santos is looking to add at least $200 million, with growth options for years to come. Among the more costly items on his agenda are a rural development program to move coca cultivators into other crops and resettle more than 6 million Colombians who have been displaced by the war, a figure making Colombia’s number of internally displaced persons among the highest in the world. The government also hopes to extend its coverage of security and services to vast areas of the country where its presence has been marginal at best.

Not everyone, both here and in Colombia, is happy about Santos’s plans, especially the deal with the Revolutionary Armed Forces of Colombia, known by its Spanish acronym as the FARC. The agreement, negotiated in Cuba over the past two years, is scheduled to be signed March 23, although Santos said that date may not be exact.

Some Republicans have questioned what they see as impunity for guerrilla leaders responsible for years of human rights atrocities, kidnappings — including of U.S. citizens — and deep involvement in drug trafficking. After a meeting with Santos on Wednesday, the House Foreign Affairs Committee chairman, Rep. Edward R. Royce (R-Calif.), said, “It is critical that the Santos government stand firm — and build upon — our hard-fought gains to combat illegal drug trafficking and disrupt terror networks.”

Retired Gen. Barry R. McCaffrey, the Clinton-era U.S. drug czar who helped formulate Plan Colombia, said in a statement that he is “concerned that the pending Colombian deal . . . could maintain or increase cocaine and heroin production, ease transit restrictions and enforcement, keep enormous profits for the FARC, worsen the heroin crisis in our country, threaten the security of Colombia, and increase U.S. drug abuse.”

Criminal trafficking networks, many of them long allied with the FARC, are positioning themselves to take over the drug business once the guerrillas, many of whom are expected to join them, formally exit the scene.

Among Democrats and human rights organizations, there is concern that the deal also offers impunity for the Colombian military and paramilitary figures who committed their own atrocities in the 50-year guerrilla war — some of it with U.S. advice and assistance.

“The failure to ensure proper accountability and punishment would undermine efforts for a sustainable peace in Colombia by perpetuating the country’s cycles of impunity,” José Miguel Vivanco, Americas director of Human Rights Watch, said in a statement. “If Obama is seriously committed to promoting peace in Colombia, he should call on Santos to ensure meaningful accountability for atrocities.”

Parts of the agreement already concluded call for those accused of atrocities and other illegal acts beyond the bounds of accepted warfare to be judged by a special peace tribunal, which can sentence them to up to eight years of “special conditions” that would not include prison. Still to be negotiated are agreements on disarming and demobilizing what are believed to be about 6,000 guerrilla fighters; at one time, the group was estimated to be 10,000-strong.

In an interview last weekend with Colombia’s Semana magazine, the chief guerrilla negotiator, known by his nom de guerre of Timochenko, said, “We are going to leave weapons to one side and join the political struggle,” including participation in future elections.

In an appearance Wednesday at the Wilson Center, Santos gave an eloquent defense of compromise. “From a human rights perspective, the worst thing you can have in a country is a war, and we’re stopping the war,” he said. “Transition has a price . . . but I think that the cost that justice is paying is minimal compared to the benefits from the human rights perspective. That’s why we think this is a good deal.”

For its part, the administration has voiced strong support for the agreement and accepted a number of Santos initiatives with which it has been less than pleased. Last year, he ordered a stop to the aerial fumigation of drug crops, a keystone of the U.S. anti-narcotics effort, and said that Colombia would no longer extradite indicted Colombians — most of them charged with drug trafficking — to the United States. Although the indictments are largely sealed, extradition requests for as many as 80 Colombians are believed to be pending.

Both of those decisions, the NSC’s Feierstein said, are Santos’s “right as president of a sovereign nation to make.”