The Florida Republican, who reversed his decision to quit the Senate after his losing the GOP presidential nomination, suddenly finds himself at the center of the political intrigue swirling around Donald Trump's nascent administration.

Rubio's tough questioning Wednesday of Rex Tillerson, Trump's pick for secretary of state, and unresolved doubts about the former ExxonMobil chief's nomination, present him with a set of provocative political choices.

The senator was expected to meet Tillerson on Thursday after expressing reservations over the potential top US diplomat's answers on Russia, the Philippines and Saudi Arabia -- particularly on human rights -- during Wednesday's confirmation hearing

"We're still working through it, so you know, we'll have a decision here soon," Rubio told CNN on Thursday.

In some ways, Rubio's position at the center of the Tillerson confirmation drama validates his decision to return to the Senate. At the time, the Florida senator argued that his deep interest in foreign policy and the clutch of threats to US national security justified his decision to reverse his resolve to turn his back on Washington. The Tillerson confirmation process gives him immediate platform to shape the course of the new administration's foreign policy.

In a baser sense, it also offers him an opening to exact revenge: a decision to slow or stall the Tillerson nomination would poke Trump in the eye. That might be a temptation for Rubio after he saw his presidential dreams crushed last year by the billionaire who ridiculed him as "Little Marco" during the bitter primary race.

Complication

Rubio could complicate Tillerson's nomination fight by declining to back him in a Senate Foreign Relations Committee vote. Assuming all of the panel's Democrats also oppose him, that would force Senate Majority Leader Mitch McConnell to resort to some legislative gymnastics to bring the nomination to the full Senate.

Such a step would position Rubio as an early -- and likely irredeemable -- critic of Trump administration foreign policy, particularly the President-elect's determination to repair estranged US relations with the Kremlin. But coming out against Tillerson would also threaten to diminish Rubio's future capacity to influence Trump's foreign policy from the Senate since he would immediately become persona non grata for the new administration.

A decision to come out against Tillerson would effectively see Rubio line up with Senate GOP foreign policy hawks like John McCain and Lindsey Graham. Like Rubio, McCain and Graham have yet to decide on whether to back Tillerson. Given the narrow GOP Senate majority, a decision by the trio to oppose him could doom the nomination, should all of the 48 Democrats in the Senate band together in opposition.

Rubio has come under intense implied pressure from establishment Republicans who are backing Tillerson, including former defense secretary Robert Gates and former secretary of state Condoleezza Rice. Alienating that establishment could hurt Rubio if he hopes to one day advance in national politics.

Apart from his shaky performance in Wednesday's hearing, Tillerson came across as a down-the-line establishment Republican foreign policy type who is far more conventional on key questions than the President he will serve if he is confirmed. That means Rubio has to consider whether alienating the establishment national security wing of the GOP would erode the foreign policy sway on which he has anchored his second Senate term.

He might also conclude that if Tillerson were to fail, Trump could nominate someone more in line with his own foreign policy beliefs and farther from the Republican mainstream.

Principle?

These concerns aside, there appears to be a more fundamental reason for Rubio's concern about Tillerson -- one that is often dismissed in the cynicism of Washington. It may well be a question of principle.

Rubio's questions to Tillerson on Wednesday were consistent with the way he has approached foreign policy throughout his career.

He took exception to Tillerson taking refuge in the fact that he had not yet had classified briefings on many human rights questions, judging that the nominee fell short of the sharp moral clarity Rubio believes should underpin America's engagement with the world.

The son of Cuban immigrants, Rubio has often viewed America's foreign policy through the prism of human rights and a deep antipathy towards communism and authoritarian governments.

He has spoken out in favor of Chinese dissidents, branded Russian President Vladimir Putin a "gangster" and pushed for democratic reforms in the Western Hemisphere in particular.

He told Tillerson on Wednesday he had no questions about his character or patriotism, but was troubled that he was unable to label Putin a war criminal, condemn thousands of extra-judicial killings in the Philippines under President Rodrigo Duterte's anti-drugs purge or to judge that Russian bombings of Syrians in formerly rebel-held districts of Aleppo amounted to war crimes.

"The position that you've been nominated to is, in my opinion, the second most important position in the US government, with all due respect to the vice president," Rubio told Tillerson. "It is the face of this country for billions of people, for hundreds of millions of people as well, and particularly, for people that are suffering and they're hurting."

"We need a secretary of state that will fight for these principles," Rubio said.