Last Sunday, masked men intercepted a white van carrying Venezuelan opposition leader Juan Guaido to a political meeting outside Caracas. They shoved Guaido into an SUV and sped away, taking into custody the man spearheading a bold and risky new strategy to try and reverse the country’s calamitous decline under President Nicolas Maduro.

Authorities freed Guaido after a short detention, perhaps because the incident was only meant to intimidate him, or maybe because the government is still unsure about how to deal with Guaido, who is raising the stakes in a way Maduro has not seen until now. ...