In January, the Trump administration predicted Venezuelan President Nicolás Maduro’s imminent downfall as he wrestled with an energized opposition, debilitating U.S. oil sanctions and international isolation after dozens of nations proclaimed his leadership illegitimate.

Today, Mr. Maduro appears in firm control. The opposition is grappling with a corruption scandal and its efforts to rekindle street protests have fallen flat. Venezuela’s crisis-racked economy is showing subtle signs of improvement. And governments across...