Of all Donald Trump’s cabinet nominees, none is more at risk of being denied confirmation than would-be secretary of state, Rex Tillerson.

When the CEO of ExxonMobil faces the senate committee on foreign relations Wednesday, he will not be in for a smooth ride. If the Republican party were united, Tillerson would be able to sail through. But many GOP senators are skeptical of Tillerson’s fitness for the post of the nation’s top diplomat, primarily because of his connection to Russian strongman Vladimir Putin.

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As CEO of ExxonMobil, Tillerson cultivated a close association with the man responsible for stymieing American foreign policy all around the world. In a business sense, Tillerson’s relationship with Putin is understandable. He runs an oil company and Russia has lots and lots of oil. CEOs of companies are responsible for maximizing profits, not for making sure their business partners are all Miss Goody Two Shoes.

But Putin may be a step too far as a business partner, even for lifelong defenders of the free market. As Mitt Romney noted in 2012 – initially to the scorn of the Democratic establishment – Russia is the greatest geopolitical foe America faces. It has stolen land from sovereign countries and threatened America’s allies in Nato. It has intervened on the side of Bashar al-Assad in the Syrian Civil War, conducting and enabling atrocities and possibly pro-longing the bloody conflict. At home, Putin has curtailed freedom and his political enemies have a strange habit of ending up dead. Abroad, he has sought to undermine the liberal democratic order.

Should a red-blooded American toast champagne with such a figure – should he accept a friendship award from such a leader – even if it is in his company’s economic interest?

The line must be drawn somewhere. And if the line is not at Putin, where is it? If Barack Obama nominated someone for secretary of state who accepted the Kim Jong Il Friendship Prize from the late North Korean dictator, Republican senators would have rioted, no? The North Korean dictatorship is surely crueler than Putin’s increasingly authoritarian state, no question. But few – if any –country is doing more to undermine America’s interests around the world than Russia.

So the first step for Republicans is to determine where the line of acceptability lies. If Putin doesn’t quite cross the disqualifying line as a friend for an incoming secretary of state, then the question should become, was their genuine affection between Tillerson and Putin, or was this merely a business relationship? Does Tillerson understand that Putin is a bad actor whose goal is to weaken the liberal international order? (Does Trump understand this – and care – is another question altogether.)

Perhaps Tillerson understands the threat Putin poses to the US. Who knows, it is even possible he used his access with Putin to secretly provide intelligence to America’s leaders. But senators must get to the root of Tillerson’s worldview, especially as it pertains to his “friend” in Moscow.

In Tillerson’s favor is the fact he was recommended by respected Republican foreign policy luminaries who aren’t under any illusions about Russia’s negative role in the world, like former Secretary of Defense Bob Gates, former Secretary of State Condoleezza Rice and former Bush administration National Security adviser Stephen Hadley.

“He has an understanding of some of the most difficult spots in the region because, in some sense, I think God has a sense of humor because oil and gas is placed in some of the most difficult and unstable regions of the world, and that’s, of course, where ExxonMobil, and therefore Mr. Tillerson, have had to work,” Hadley told me in a December interview for my podcast.

Now it is true that ExxonMobil is represented by Rice, Hadley and Gate’s international consulting firm, but these are American patriots in the truest sense and it is hard to believe they would recommend someone for such a crucial position that they didn’t believe had America’s best interests in mind.

Nonetheless, at a time when Russia stands accused of meddling in our election process and the president-elect seems to have something of a crush on Russia’s strongman, the Senate must vet Tillerson to determine whether he is clear-eyed about the Russian threat. Perhaps they will determine he is hard headed and his relationship with Putin is an asset. Perhaps not.

What’s certain is it won’t be a cakewalk for Tillerson. If Florida senator Marco Rubio votes “no” in committee, as is imaginable, that could end Tillerson’s nomination right there. But Republican leaders could use procedural moves to get Tillerson a floor vote anyway. If Rubio votes “no,” you can be sure that Republican Tillerson skeptics like John McCain and Lindsey Graham will vote “no” on the floor, which would be enough to defeat Tillerson unless there is a Democratic defection in support of him (from, for example, West Virginia senator Joe Manchin).

The point is, unlike a lot of the other confirmation hearings, Tillerson’s is not perfunctory. His relationship with Putin could destroy his candidacy. So could reports that an Exxon subsidiary did business with Iran. He will have to answer for all this and more.

You can bet that Putin and Trump will be watching – as will the man who might benefit most from Tillerson’s implosion, Mitt Romney.