After finding refuge and building power in Venezuela, a decades-old rebel group has waged the worst violence in Colombia in a generation, setting off troubling regional tensions.

There were no Situation Room meetings and no quiet calls to de-escalate a dispute with an ally. Just threats, counterthreats, surrender and an indication of the president’s approach to Greenland and Panama.

The country’s leader, Gustavo Petro, backed down after a clash with President Trump, which started when Mr. Petro turned back U.S. military planes carrying deportees.

Clashes between armed groups in Colombia have led to some of the worst violence in the country in years.