Nearly three weeks after the Trump administration backed an all-out effort to force out President Nicolas Maduro, the embattled socialist leader is holding strong and defying predictions of an imminent demise.

Dozens of nations have recognized opposition leader Juan Guaido’s claim to the presidency and the U.S. has tightened sanctions aimed at cutting off billions of dollars in oil revenue. But anti-Maduro street protests have come and gone, and large-scale military defections have failed to materialize.

With the U.S. seen as considering military action only as a last resort, Guaido is trying to regain momentum with an effort this week to move U.S. emergency food and medicine into Venezuela despite Maduro’s pledge to block it.

Such an operation could provoke a dangerous confrontation at the border — or fizzle out and leave Maduro even stronger.

With so much at stake, Guaido is under increasing pressure to soon unseat Maduro, analysts say.

“He is running against the clock,” said Daniel Lansberg-Rodriguez, a Venezuela expert at Northwestern University’s Kellogg School of Management. “Expectations are running very high — not just among Venezuelans but international allies — that this is a crisis that can be resolved quickly.”

Despite having the world’s largest oil reserves, Venezuela is suffering soaring levels of malnutrition, disease and violence after 20 years of socialist rule launched by the late President Hugo Chavez. Critics accuse Maduro, a former bus driver and Chavez’s hand-picked successor, of unfairly winning an election last year for a second six-year term by banning his popular rivals from running and jailing others.

The 35-year-old Guaido was a virtually unknown lawmaker until last month, when he took the helm of the opposition-controlled National Assembly. He has rallied masses of Venezuelans into street demonstrations that have left at least 40 dead since he declared himself interim president on Jan. 23.

Guaido has so far avoided arrest, but the general comptroller announced Monday it was opening an investigation into Guaido’s assets in a new escalation of the confrontation between the government and the National Assembly.

Guaido has won backing from nearly 50 countries worldwide, including the United States, which has pledged an initial $20 million in support and has already shipped emergency food and medicine to the Colombian border city of Cucuta, where it sits in a warehouse.

Maduro has refused all economic assistance, denying there is an economic crisis in Venezuela — and contending the aid is part of a coup being orchestrated by the White House to topple him.

Maduro has made a show of overseeing military operations played on state TV almost daily. He’s jogged with troops in formation, mounted an amphibious tank and railed against what he says is an impending U.S. invasion that he has likened to a Latin American Vietnam.

On Monday, Venezuela socialist party chief, Diosdado Cabello, spoke at a rally in Venezuela’s border city of Urena, across from Cucuta, crowding the streets with Maduro loyalists wearing the red shirts of the socialist party and waving flags.

Addressing the crowd, Cabello asserted Venezuelans tell him not to give in to pressure from the United States, saying they are willing to endure whatever they must to maintain freedom from imperialist rule. He said the U.S. supplies were sent in a showy display aimed at justifying a coup.

“It’s not help and it’s not humanitarian,” he said to cheers from roughly 1,000 Maduro supporters, including civilians and soldiers.

Romulo Jaimes, a 62-year-old resident of Urena, said the socialist gathering wasn’t what it appeared to be. He said more than 30 buses were parked outside the event, used to haul in Cabello’s cheering crowd.

“In reality it was a flop,” he said. “Most of the people from this city didn’t attend the rally.”

The U.S. humanitarian aid is being stored in a warehouse across a river from the socialist rally, a situation that also puts Maduro in a tight situation, said Eric Farnsworth of the Council of the Americas and Americas Society, a Washington-based think tank.

“If you let it in, you’re bowing to Guaido and the international community,” he said. “If you don’t you’re seen as a tyrant.”

President Donald Trump has said all options are on the table regarding Maduro’s ouster, but Farnsworth called any U.S. military deployment highly unlikely as such a move would make the U.S. responsible for supplying food long term and rebuilding the gutted country.

U.S. sanctions imposed on the state oil company PDVSA in late January and meant to pressure Maduro from office have yet to bite. In the capital, Caracas, residents pulling up to gas stations can still fill up their cars, despite fears that sanctions would create shortages.

Opposition leaders have been vague about how they plan to get the aid in.

Last week, Lester Toledo, Guaido’s representative in the aid mission, suggested it could be moved by masses of people converging on the border to carry the food and medical supplies across.

On Monday, Guaido posted a video on Twitter showing himself and his wife making phone calls urging people to join a volunteer force by registering on a website and calling on them to return to the streets in protest Tuesday. 

“We’re working hard,” he said in one call. “Not only to bring in the aid, but also to end the tyranny” of Maduro. 

Gaby Arellano, an opposition leader who is among those leading the aid mission, said the strategy was to conduct “defiance” politics, which she said consists of setting an agenda that forces Maduro’s hand, though she provided no details.

“We are politically defining the steps and they are responding to what we put forth,” Arellano said. “We want and are working for this to be as peaceful, least traumatizing and as quick as possible.”

Amaliexiz Mendoza, who lives in Cucuta with her 3-year-old daughter among the city’s large Venezuelan exile community, said she would walk a thousand times to carry humanitarian aid to her countrymen. Her grandmother, an aunt and young cousins still live in Venezuela and often go hungry, and her grandmother can’t get the blood pressure medication she needs.

“It’s not right for a child to go to bed hungry,” Mendoza said, tearing up as she spoke of Maduro’s denial that a crisis exists. “He doesn’t lack anything but our families do.”