Marco Rubio’s confirmation hearing begins a new chapter in the political career of the 53-year-old Florida Republican, whose relationship with Trump has evolved over the last decade. Once rivals trading schoolyard insults as they campaigned for president in 2016, the two men became close allies as Trump campaigned for another White House term last year.

Unlike many of Trump’s Cabinet selections, he is expected to easily win confirmation, notching support not only from Republicans but also Democrats who endorse him as a “responsible” pick to represent the U.S. abroad. Many expect Rubio will be among the first of Trump’s Cabinet picks approved.

If confirmed, Rubio will become the leader of U.S. foreign policy — though his role will surely remain secondary to Trump, who relishes the global stage and frequently uses the bully pulpit against America’s allies.

Secretaries of state have played a key role in formulating the foreign policy of the country since its founding, starting with the first one, Thomas Jefferson, who served in the top Cabinet position under President George Washington.