The most interesting person to watch in ExxonMobil CEO Rex Tillerson’s confirmation hearing for secretary of state Wednesday — after Tillerson himself — is without question Sen. Marco Rubio (R-Fla.).

The Florida Republican is likely to reveal what kind of future he wants in President-elect Donald Trump’s Washington, and there are two broad possibilities. He could play a lead role in trying to torpedo Trump’s pick for the nation’s top diplomat, by turning his question-and-answer sessions with Tillerson into an aggressive attack on his economic ties to Russia and the honors bestowed upon him by President Vladimir Putin.

Or Rubio could be, well, more diplomatic, tempering his questions about Tillerson’s global philosophy and Trump’s own views toward Putin and paving the way for an easy confirmation.

Rubio’s fellow hawks on national security issues will be watching closely to see which path he takes. Several of them have joined Rubio in criticizing Tillerson’s credentials, but Rubio is the most prominent among them on the Senate Foreign Relations Committee, which is tasked with vetting the oil titan’s qualifications. That puts equal parts of pressure on Rubio to voice that perspective — and to be careful about his relationship with the incoming administration.