John McLaughlin is the former deputy director of the CIA. He writes a regular column on OZY called “Global Eye: Foreign Affairs Through an Intelligence Lens,” and teaches at the Johns Hopkins University’s School of Advanced International Studies (SAIS).

The author was deputy director and acting director of the CIA from 2000 to 2004 and currently teaches at the Johns Hopkins School of Advanced International Studies (SAIS).

If you want a clue as to how Donald Trump will deal with Russia, just keep a close eye on Ukraine.

Anxiety is swirling over this week’s killings in Europe, including the assassination of Russia’s ambassador in Turkey. But what happens in Ukraine over the next year will be among the first indicators of whether the Trump administration is prepared to tolerate Russian advances in Europe — and whether it is committed to the global order we have defended for decades — or whether he has something else in mind.

Almost exactly three years ago, as protests roiled Kiev, I argued that OZY readers should follow the fate of Ukraine. And much has happened since. Four months after that article, Russian President Vladimir Putin snatched Crimea. Then he invaded eastern Ukraine, where his forces are still present and fighting.

What drives Putin on Ukraine? At least three things:

1. A Democratic Ukraine Threatens Putin’s Russia

“Ukraine is the only former member of the Soviet Union that can change Russia” — that’s what a young Ukrainian politician said to me during my visit to Kiev in October. In other words, Putin’s iron control would be severely challenged if Ukraine achieved European-style democracy and prosperity based on an open system in which corruption was severely curtailed or eliminated. Why? Because many Russians see Ukrainians as a mirror image of themselves, as their Slavic “little brothers and sisters.” In the face of democratic progress in Ukraine, many Russians would be asking: Why not me? Why are we putting up with limited democracy, a controlled press and rampant corruption if little Ukraine has slipped the noose?

In short, Putin smells danger to himself and his system if Ukraine falls out of his orbit and into Europe’s.

2. Anger Toward the United States

Putin believes, wrongly, that the United States was behind the series of Ukrainian revolutions that since 2004 have called for more democracy. One former Ukrainian official told me that he heard Putin threaten way back then to take Crimea and Donbas (eastern Ukraine) if Ukraine ever joined Europe or NATO. The trigger for grabbing Crimea appears to have been precisely that — the 2014 Ukrainian plan for a referendum on an association agreement with the European Union (EU).

3. Plummeting Oil

Finally, Putin can no longer count on rising oil prices to guarantee prosperity and his popularity, as he did during his early presidential years from 1999 to 2008. Now that Russia’s economy is faltering, he relies on foreign adventures such as Ukraine and Syria. Such actions tap into a nationalistic strain that yearns — coining a phrase here — to make Russia great again.

Against that backdrop, Ukrainians I’ve spoken with are alarmed that President-elect Trump’s talk of a closer relationship with Moscow means he would let Putin off the hook for what he did in Ukraine. To be fair, there is nothing inherently wrong with wanting a less conflictual relationship with Russia, with which the U.S. does share some interests. The key question is: Have we defined our interests clearly enough to know what we want in return?

We had better, because Putin has a very clear idea of what he wants. His needs fall into two categories. One is fairly easy to satisfy; the other less so. The easy one: Numerous Russians tell me that what Putin craves most, just like Aretha Franklin, is respect. It’s very personal with him; he wants to be treated as an equal by leaders of the world’s great powers, not shunned or relegated to the sidelines. This is probably why Putin has responded so well to Trump’s compliments.

The second set of Putin “wants” is harder. He wants a freer hand to operate in what he regards as Russia’s natural sphere of influence, which extends to most of the countries along Russia’s border — starting with Ukraine. He’d like the U.S. and Europe to lift the tough sanctions they’ve imposed on Russia. And he’d like to see Ukraine grant enough autonomy to its eastern provinces — home to many ethnic Russians — that they are able to block further integration into Europe. Ukraine resists this and does not want to negotiate further without an internationally monitored cease-fire, which has not yet come about.

The problem with accommodating Putin on Ukraine is clear. His invasion violated at least three international treaties on the sanctity of European borders. The U.S. is signatory to two of those treaties, one dating to 1975 and the other to 1994. Ukraine in 1994 surrendered nuclear weapons to Russia in return for a U.S./U.K./Russian pledge not to violate its borders.

This is the tough thicket the Trump administration will enter as it develops its Russia policy. If it simply gets out of Putin’s way, Trump will be kicking out some key pillars of post–WWII European stability. Before doing so, the administration will need to know what to put in its place. And it had better have some understanding of what Putin would do elsewhere — in the heavily ethnic Russian Baltic regions of NATO for example — if he sensed softness on our side. And what would NATO’s military response be if Putin did then push harder against the Alliance’s red lines?

Where will the Trump team go with these issues? Watch Ukraine. For these questions, it is the canary in the mineshaft.