Until a few weeks ago, it looked like the upcoming Summit of the Americas in Panama would be a golden opportunity for President Barack Obama to seal his announced normalization of ties with Cuba, and remove a decades-long sore point in U.S.-Latin American relations. But with few days to go before the 34-country summit, Obama’s prospects of emerging a big winner look bleak.

Several developments in the past few weeks will put Obama on the defensive at the mega-summit, a rare occasion where the U.S. president will meet collectively with all his Western Hemisphere counterparts. Since the first of these meetings was held in Miami in 1994, they have taken place only every three or four years.

First, the March 9 Obama executive order denying U.S. visas and freezing U.S. assets of seven Venezuelan government figures accused of human rights abuses or public corruption has led Venezuelan President Nicolás Maduro to seek 10 million signatures demanding the sanctions be repealed. Maduro has said he will present the massive petition to Obama in Panama.

While Maduro’s petition drive is characteristic political theater to divert attention from Venezuela’s domestic problems, and the Obama administration has repeatedly said — contrary to Maduro’s assertions — the U.S. sanctions will not affect the Venezuelan population, the U.S.-Venezuela dispute will dominate news in much of Latin America.

A second likely spoiler of the Obama-Castro fiesta could be Cuba itself. Cuba’s military dictator cannot afford not to openly support Venezuela at the summit, for economic and political reasons. Venezuela remains Cuba’s main economic benefactor, and Cuba anti-imperialist narrative remains the main justification for Castro’s refusal to allow free elections on the island.

A third possible spoiler of the Obama-Castro fiesta will be Cuban dissidents, who felt sidelined by Obama when he announced his Dec. 17 offer to normalize ties with Cuba.

Guillermo Fariñas, a leading Cuban dissident who hopes to be at the Panama summit’s civil society forum, told me in a telephone interview from Cuba that unless Obama demands Cuba at the summit to take concrete steps toward democracy, “we will be very disappointed.” Among other things, Obama should demand that Cuba free political prisoners, stop beatings of government opponents, and allow freedom of assembly, Fariñas said.

Granted, Obama will have some things playing in his favor in Panama. Unlike in previous Summits of the Americas, where Venezuela was riding high on booming oil prices and Brazil and Argentina had significant diplomatic clout in the region thanks to their own commodity price booms, the upcoming summit will take place in a very different world scenario.

Today, with declining commodity prices, Venezuela’s economy is expected to contract by 7 percent this year, Argentina’s economy is projected to decline by 2 percent, and Brazil’s by 1 percent — its worst economic performance in the past 25 years. And the presidents of Brazil, Argentina, Venezuela and several other U.S. critics in the region are at their lowest popularity rates ever.

So what should Obama do at the Summit? Some U.S. summit observers say that appearing in a smiling picture alongside Cuba’s Castro, and in another one with Cuban dissidents, will suffice to make Obama the star of the summit. That, alongside his tentative deal with Iran, will portray him as a global peacemaker, they say.

My opinion: It won’t work that way. While U.S. media attention will be focused on the Obama-Castro embrace, much of Latin America’s attention will be focused on the U.S. sanctions against Venezuelan officials.

To come out as a winner, Obama should be bold. When Maduro does his theatrics and presents Obama with a document purporting to have been signed by millions of people — most of them Venezuelan public employees who have been forced to sign it — Obama should respond in kind.

Rather than being taken by surprise and accepting it with a smile, as he did when late Venezuelan President Hugo Chávez presented him with a book blaming the United States for all of the world’s evils at a similar summit in 2009, Obama should present Maduro with a copy of the United Nations Universal Declaration of Human Rights.

While doing that, Obama should demand that Venezuela’s legislative elections scheduled for later this year take place with a credible electoral tribunal, trustworthy voting lists, without media intimidation and with equal television time for opposition candidates.

And instead of meeting with Cuban dissidents on the sides of the presidents’ summit, as he now plans to do, Obama should surprise the world by giving a Cuban opposition or human rights leader five minutes of his time during the summit’s plenary session. That would help disarm critics — especially in the U.S. Congress — who have doubts about his stated commitment to human rights in Cuba.

If Obama doesn’t do something bold, he will be upstaged by a military dictator and a few populist demagogues, and what U.S. officials expected to be a legacy-setting summit will turn out to be a diplomatic fiasco.