CÚCUTA, Colombia — Border standoffs may not get much stranger than this one.
Three presidents, a military plane and a lineup of pop artists brought by a British billionaire arrived at a border city known to few before it became famous as the site of a military blockade by Venezuela’s defiant president, Nicolás Maduro.
Mr. Maduro was determined to keep foreign aid out of his country, and the Venezuelan opposition saw an opportunity. Their plan: to break the blockade on Saturday, a culminating act of defiance meant to force the military to choose between allowing food into a hungry nation and loyalty to Mr. Maduro.
It did not go well. By the end of the day, the military had largely sided with the regime, and a protest planned as peaceful had descended into violent skirmishes. Some of the desperately needed aid was burned at the border, and four people were reported dead.
It was Mr. Maduro who had made the first move.
Earlier this month, as food donated largely by the United States made its way to the Colombian border town of Cúcuta, his government barricaded an already-closed border bridge between Colombia and Venezuela, using tanker trucks and containers.
The president’s defenders accused the Americans of trying to foment a coup with the aid — a kind of Trojan horse, they said. The intent, they said, was not to relieve Venezuela’s hunger but to destabilize the Maduro government.
With the border sealed, the political skirmishing intensified — and the focus was on the aid piling at the border.
Among the first to visit the shipment from the United States Agency for International Development was Senator Marco Rubio, the Florida Republican who has called for regime change in Venezuela. After making a tour of the supplies, he headed to a bridge where he denounced the leftist government and called on the military to turn against its leaders.
On Friday, the day before opposition supporters planned to break the blockade, the mood of the standoff took a turn with the arrival of Richard Branson, the British entrepreneur. Mr. Branson had invited Latin American pop artists to play a concert to benefit Venezuelans.
The show, which took place on the border bridge where the supplies had been staged, was part musical gathering, part political rally as celebrities and concertgoers took to the microphone to condemn the Maduro government.
The next morning, Saturday, Mr. Guaidó took center stage, hopping on board an aid truck and vowing that it would enter his country.
The day began peacefully.
Many demonstrators awoke in an empty lot where they had camped overnight, and a member of the clergy offered a prayer for their safety. They then slowly made their way to the bridge.
Their plan: to accompany the aid on foot, in the form of a human shield, holding roses and singing the Venezuelan anthem.
But things quickly turned chaotic.
After national guardsmen began firing tear gas at the protesters, hope of an agreement between the two sides seemed to slip away.
Soon demonstrators were hurling rocks back at the soldiers, a descent into the kind of violence that has stymied past protest movements in Venezuela.
As the storm was brewing, Mr. Maduro and his wife, Cilia Flores, were far from the border, and enjoying another sort of day. They held a rally where they danced salsa before supporters.
At the bridge, the chaos only grew.
Scores of Venezuelan national guard members began to defect into Colombia, some coming in with wounds. They crossed under the border bridges to the cheers of crowds.
And some of the aid had begun to make it through.
But amid the skirmishes, the exploding tear gas canisters from Venezuelan security forces and the fire bombs from protesters, a blaze broke out. It destroyed boxes of what one opposition lawmaker said were medical supplies destined for Venezuelan hospitals.
What the opposition had hoped would be a day of peaceful protest had turned deadly. Four people were killed, and many others were arrested and taken to Venezuelan jails.
Mr. Maduro, enraged at the help President Iván Duque of Colombia had given protesters, cut off diplomatic ties with Colombia.
Eventually, the crowds abandoned the bridge, but some young men remained to keep fighting, throwing stones and hurling homemade bombs at government forces.
Tear gas was still wafting over the border as the aid trucks were taken back into warehouses on the Colombian side. The battle between opposition and regime once more appeared to be at a stalemate.
And the political standoff seemed to have come full circle.
Venezuelans were in as much need of food as ever, the aid was sitting useless in Colombia, and Mr. Maduro appeared to remain fully in power.
Things had changed, however, for Mr. Guaidó.
He was not able to cross back into Venezuela with the aid, as he had promised. And now he was in Colombia. It was unclear whether Mr. Maduro would permit him to return.