DAVOS, Switzerland — This time last year, Juan Guaidó would have been the toast of Davos. Mr. Guaidó, the Venezuelan opposition leader, had just led a wave of popular unrest to win the presidency of Venezuela’s National Assembly and declared himself the true leader of his crisis-ridden country.

But as Mr. Guaidó made the rounds at this year’s gathering of political and business figures — having come to Europe in defiance of a travel ban at home — he seemed like a man whose moment had passed.

With Venezuela’s repressive president, Nicolás Maduro, still firmly entrenched in power, and with Mr. Guaidó’s most prominent backer, President Trump, distracted by his Senate trial and his re-election campaign, the embattled Venezuelan spent most of his time answering questions about why he had not succeeded in toppling Mr. Maduro.

“We underestimated the ability of the regime to do bad,” Mr. Guaidó told a half-filled hall where, two days earlier, Mr. Trump had spoken to a standing-room-only crowd. “We are really climbing a mountain at the moment.”