It was not so long ago that Donald Trump and Marco Rubio were bitter enemies. During the 2016 primary, Rubio called Trump a “con man” and suggested that he had wet his pants during a debate. In return, Trump dubbed the Florida senator “Liddle Marco,” questioned the Cuban-American’s citizenship, and mocked his 2013 response to Barack Obama’s State of the Union address, in which he had to interrupt his televised speech to chug a very small bottle of water. “‘I need water. Help me,’” Trump croaked in a campaign speech mimicking Rubio, before calling him a “choke artist.”

Rubio is hardly the first Republican critic of Trump to do a grinning about-face once Trump secured the presidential nomination and went on to win the election. But more than most opportunists on Capitol Hill, Rubio has used the Trump presidency to elevate his stature and amass power. To an unprecedented degree for a lawmaker, he is directing the government’s approach to an entire region: Latin America. It’s a part of the world that has long been subject to the whims of U.S. foreign policy—now, those whims increasingly belong to one man.

Consider that, until recently, the Trump administration showed deep apathy toward Latin America. While Barack Obama and George W. Bush had each made a handful of trips to the region by this point in their first terms, Trump did not travel to Latin America until November, to the G-20 summit in Buenos Aires. Last year, he canceled trips to Lima and Bogotá, and he has yet to visit Mexico, sending his daughter Ivanka Trump to the December inauguration of Mexico’s new president in his place. Eleven out of 28 diplomatic posts in Latin America and the Caribbean remain empty. An assistant secretary of state for Latin America was not finalized until October, nearly two years into Trump’s first term.

But indifference turned to enthusiasm on January 23, when in a rebuke to Venezuelan President Nicolás Maduro, Trump recognized a 35-year-old right-wing upstart named Juan Guaidó as the country’s legitimate leader, a move that The Wall Street Journal described as the “first shot in [a] plan to reshape Latin America.” The force behind the Trump administration’s move was Rubio. In the absence of a clear policy for the region, The New York Times has called Rubio “a virtual secretary of state for Latin America.” On Cuba policy, to name one egregious example, Trump reportedly has offered his National Security Council little guidance but to “make Rubio happy.”

The son of Cuban émigrés who cemented his personal and political identity around antagonism toward the Castros, Rubio has hounded Trump to take a hardline stance against the so-called “troika of tyranny”: Venezuela, Cuba, and Nicaragua. This agenda includes ousting Maduro from the presidential palace in Caracas, lifting the Obama-era detente with Havana, and supporting the popular movement against Nicaraguan President Daniel Ortega and his leftist Sandinista Party in Managua.