A woman has died in clashes between protesters and security forces in Venezuela.
Dozens of people were injured in the latest day of protest in the country.
However, those expecting the population to answer opposition leader Juan Guiado's call for the "largest march" in the country's history were largely disappointed.
He has now called for an escalating series of strikes in a bid to force President Nicolás Maduro to relinquish power.
For the third time this year, the big moment in Venezuela has turned into a bust.
Trump administration officials had expected that Wednesday might turn out to be the beginning of the end for President Maduro with senior government figures withdrawing support and the opposition launching a mass uprising with military backing.
But the promised defections did not happen, the military uprising never materialised and Mr Maduro still appeared to be firmly in command of the South American nation.
Trump officials were back to complaining about the support Venezuela receives from Cuba and Russia while issuing vague warnings of military action.
"Military action is possible," Secretary of State Mike Pompeo said in an interview on Fox Business Network. "If that's what's required, that's what the United States will do."
It was another reality check for an administration that has thrown its support behind the opposition with a series of diplomatic and economic measures that, so far at least, have failed to achieve their goal of ousting Mr Maduro.
The US views Mr Maduro's re-election last year as fraudulent and illegitimate and has recognised Juan Guaido, the opposition head of the National Assembly, as interim president.
Some in the administration thought they would achieve their mission in January, when the US formally recognised Mr Guaido and around 50 other nations followed suit.
Others thought it might end in February, when the opposition entered the country with trucks of US aid to help the people of a once prosperous country where many now go without food and medicine amid a deep economic crisis.
This week, administration officials were told the defence minister, the president of the supreme court, the head of the presidential guard and others would formally announce that they supported the Venezuelan constitution, implicitly backing the opposition, said Elliott Abrams, the special US envoy for Venezuela.
It was "widely understood", Mr Abrams told reporters at the State Department, there would be huge May Day marches and Mr Guaido and his supporters hoped they "would lead peacefully to the end of the Maduro regime".
Instead, US officials were caught off guard early on Tuesday with the release of a video featuring Mr Guaido and Leopoldo Lopez, an opposition leader who suddenly appeared to have been freed from house arrest with the cooperation of soldiers guarding him.
They called for a mass uprising with the military, dubbed "Operation Freedom".
But the security services that have backed Mr Maduro throughout the crisis never switched sides to any notable degree.
The defence minister, Vladimir Padrino, reaffirmed his support for the government early in the morning. By the end of the day, Mr Lopez and his family had sought refuge in the Chilean ambassador's residence and then the Embassy of Spain.
US officials said Mr Maduro would never be able to hang on without the support of Russia and Cuba, which they say has some 20,000 military and intelligence personnel in the country.
Cuba angrily denied the allegations, saying the vast majority of its roughly 20,000 people in Venezuela are providing health care, education and basic infrastructure services.
"To the allegations that Cuba has troops in Venezuela, they are totally and absolutely false," Cuba's director-general of US affairs, Carlos Fernandez de Cossio, told The Associated Press in an interview in Washington.
"Cuba does not participate in military operations or security operations in Venezuela of any type."
On the ground in Venezuela, the situation remained unsettled and unclear.
Mr Trump's top national security aides, including Mr Pompeo, national security adviser John Bolton and acting Defence Secretary Patrick Shanahan, who cancelled a trip to Europe to work on Venezuela, huddled at the White House to discuss possible options.
Those options should not include the US military, said Representative Eliot Engel, a New York Democrat who is chairman of the House Foreign Affairs Committee and was briefed by Mr Pompeo and Mr Bolton on the situation.
Mr Engel, who recently visited Venezuelan refugees on the Colombia border and believes Mr Maduro should go, said Congress has too often gone along with military adventures abroad.
"I think the days when the United States can intervene and send in the Marines are over and should be over," he said.