"With Chavez no longer on the scene, and the power vacuum exposed, the situation becomes extremely unpredictable," Shifter said. "The fact that Maduro is Chavez's designated successor gives him the upper hand for the time being, but that is unlikely to last long. The others vying for power are wily and ruthless. From the outset, the Chavez regime has been about power — including lots of money — and now all of that is up for grabs."
Maduro and Cabello, for their part, projected a united front this week by appearing together at events along with other Cabinet ministers and military commanders. Speaking alongside Cabello and others Wednesday, Maduro said: "We're more united than ever."
Maduro was somber-faced as he warned that Chavez faced a "complex and hard" recovery period.
But at a rally on Thursday night, Maduro apologized for having shown sadness. "Our faces are an expression of the pain, the worry, the purest love that we feel for Hugo Chavez," said Maduro, whose voice was hoarse as he shouted to the crowd.
The government said in its statement that "additional specific treatments are foreseen in order to contribute to the full recovery of his health."
The 58-year-old president underwent his fourth cancer-related operation in Havana after announcing that tests had found the illness had come back despite previous operations, chemotherapy and radiation treatments.
Several outside medical experts have said that based on Chavez's account of his condition and his treatment so far, they doubt the cancer can be cured. Some cancer experts say Chavez could be suffering from an aggressive type of sarcoma.
If Chavez were to die or be unable to continue in office, the constitution says that new elections should be held within 30 days. If that happens before the swearing-in, the president of the National Assembly is to take over temporarily until elections are held.
Before his surgery, Chavez acknowledged such a scenario. He said on television, with Maduro and Cabello seated beside him, that if he is unable to continue on as president, Maduro should be elected to take his place and lead the socialist movement.
On Caracas' traffic-clogged streets, people were busy with pre-Christmas shopping and the government put up new banners on lampposts reading "Now more than ever, with Chavez."
While some of his supporters expressed fears about a messy succession battle, others said the people wouldn't stand for it.
"I trust Chavez's allies aren't going to end up fighting if El Comandante leaves us," said Mariana Salas, who sells orange juice and fruit on a sidewalk in the working-class neighborhood of Petare. "If it turns out that some of them do, they should be expelled from the party because Chavez gave a very clear order: Maduro is the man we should follow."
Noel Perez, who opposes the president, said he thinks that if Chavez dies, "the Chavez movement ends, it's that simple."
Associated Press writers Christopher Toothaker and Fabiola Sanchez in Caracas, Michael Warren in Buenos Aires, Argentina, and Frank Bajak in Bogota, Colombia, contributed to this report.
Ian James on Twitter: http://twitter.com/ianjamesap