President took the Oval Office today with the most anti- outlook in recent memory. His previous that he might not assist our allies if they came under attack, as required under under the North Atlantic Treaty, which has been particularly troubling to America’s European allies. Ominously missing from his speech was Russia, which some critics credit with undermining the election itself.

During his inauguration speech, President Trump said little about defense or engaging other countries other than committing to protecting “our borders from the ravages of other countries.” His “America First” philosophy is a major shift from America’s post-World War II mindset where the U.S. sought to be a kind of police force around the globe; President Trump seems to hint at his America taking on a more isolationist mindset.

But with Russian President Vladimir Putin aggressively harassing Ukraine and the Baltics, one has to wonder who in Washington will defend Eastern Europe and NATO now.

Donald Trump will be the President of the United States in just a few weeks, and it’s anyone’s…

President Barack Obama was the most aggressive opponent of Moscow’s expansionism since the fall of the Soviet Union—particularly when you consider his response to the Kremlin’s actions in Ukraine. His coordinated efforts with the European Union to sanction Russia over its annexation of Crimea taxed its economy so severely that it 3.7 percent in 2015; last year its GDP was expected to further contract 1.2 percent.

The sanctions have also Russia from raising billions in needed western currency for its oil and gas exploration projects in the Arctic Circle, forcing Moscow to scramble for cash in Beijing, whose as those in European capitals.

A Zero-Sum Game

None of this warmed relations between the Kremlin and the White House, but that was inevitable—Eastern Europe is a zero-sum game for Putin and Obama refused to acquiesce its security. Putin, the former KGB officer, wants to expand beyond Crimea and into the rest of Ukraine and beyond, according to political analyst Alastair Newton.

“Rising domestic socioeconomic stresses in Russia—caused by dwindling oil revenues and the impact of Western sanctions—will fuel President Putin’s anti-western rhetoric and increase the likelihood of him seeking foreign ‘distractions’,” Newton, told last year. “We therefore expect Russian provocations in its ‘near abroad’ to continue, including in NATO territory, short of an outright ‘land grab’.”

Retired U.S. Army General Jack Keane warned that Putin has plans to invade the Baltics. “The Russians are (now) putting considerable pressure on the Baltic States, with the very real possibility of challenging NATO with a military hybrid occupation similar to eastern Ukraine, Keane told the . (Keane told the paper he declined an offer to be Trump’s Secretary of Defense.)

But, so far, Russian troops have not advanced pasteastern Ukraine. No matter what Obama’s detractors may have said, his coordinated sanctions with Brussels did in fact work. Russian troops may be in Ukraine, but they aren’t sipping vodka in the middle of Independence Square in Kiev—even though Russia could go much deeper into the country, if it desired to do so.

Ukraine has 200,000 service members; Russia has an 766,000 active duty and 2.5 million on reserve. There is no comparison. Putin is not advancing any further because he expects a potential response from the west, even if it is not a military one.

However, what is becoming dangerously clear with each overture Trump extends to Putin is that the security of Eastern Europe and the integrity of NATO is in dire jeopardy. In fact, Trump’s stated affections for Putin reveal that the new president may give in to his future Russian counterpart’s desire for NATO to stay outside of Moscow’s “sphere of influence” and allow him to run wild there—even though he has not outlined what getting along with Putin would actually look like.

The fact that Russia absorbed much of eastern Ukraine, and little was asked of how Trump planned to prevent Putin from expanding further, have left us with few clues on how Trump would handle the ongoing crisis there. But we can highlight some key steps Trump should consider, if he wants his foreign policy to reflect his get-tough bluster.

How To Handle The Russians

For starters, Putin must know that if he even thinks about invading the Baltic republics of Latvia, Estonia and Lithuania, the move will leave a far more crippling wound on Moscow than NATO.

Russia recently deployed Iskander tactical ballistic missiles to its Kaliningrad region, which borders Baltic states of Lithuania and Latvia. These missiles have a range of at least 500 kilometers and are designed to destroy strategic targets. What’s more, they can carry nuclear warheads and have an error point of just 10 kilometers. Washington claims the move the Intermediate-range Nuclear Forces Treaty that forbids such offensive weapons. Under Article 5 the United States is required to shore up military support for the Baltics in the event of an attack; the Baltics do not have the military strength to fend off a Russian offensive, RAND report. The Baltics only have 11 battalions between them compared to Russia’s 46, which includes tanks, surface-to-surface missiles, Marines, and other heavily armed units and hardware. Another problem is that Russia shares a border with the Baltics and can easily deploy reinforcements into its territories.

A high-ranking Department of Defense official Congress in June that Russia could take the region’s capitals in less than 60 hours, and that more battalions are needed to prevent a complete overrun. Some 4,000 U.S. troops in Poland a few days ago as part of a show of force rotation Obama ordered more than a year ago. Other EU nations to sending more personnel to help bolster its military presence in Poland and the Baltics. All of these steps are highly unusual for a military during peacetime and are clear indications that NATO is preparing for a possible attack.

It ought to. Putin .

Encouraging America’s NATO allies to follow through on their deployment commitments should be one of Trump’s first priorities after entering office. Indeed, Trump spent much of the campaign suggesting he would not honor the NATO treaty but, in practice, he’ll soon learn that alienating the alliance will not work. If Putin pulls the same hybrid warfare in the Baltics as he did in Ukraine (), Trump will be assailed as weak for allowing it to happen.

Putin knows our incoming president will be less interventionist in Eastern Europe as Obama, which is why Baltic leaders have raised fears over Trump’s presidency. All Estonia, Latvia and Lithuania know is they aren’t getting a president who appreciates its security issues.

The possibility of Putin invading the Baltics is real. Many traditional foreign policy observers didn’t believe Putin would invade Georgia in 2008, but he did. Few thought Putin would annex Crimea, but it happened. It is assumed that Putin would not attack a NATO country because of the military alliance. But given that Trump has been very hostile towards NATO, who is to say that Putin won’t invade when his past actions prove otherwise?

If Putin does, in fact, wage an attack against the Baltics in 2017, it will signal to the world that Russia can crack the armor of the world’s most powerful military and that America’s Eastern European NATO allies’ security is tenable.

Over the past two years, Obama fended off accusations of weakness regarding his response to Russian aggression, even though his sanctioning of key Russian economic institutions are actions President George W. Bush did not take when Moscow invaded Georgia in 2008. And those who said Obama should have done more to punish Putin over Ukraine, they never really articulated what more, exactly, looked like.

Why Intervene At All?

The consequences of America not taking on Putin could be disastrous for several reasons. For one, fighting in eastern Ukraine is ongoing and a full-scale war again. That war can potentially spread over into the Baltics, which have large populations of Russians under the premise that Moscow is protecting its people; the Kremlin . Latvia, for example, has concern that its large Russian population could give Putin a reason to invade under a similar premise.

And if Putin were to invade the Baltics, it would move his military sphere of influence squarely into Western territory. If Russian troops can enter Estonia or Poland, in theory, why not Germany as well? Of course, the first thought is to assume that it cannot happen. But given Trump’s distain for NATO, such a possibility is very real and America’s allies have over his indifference to their security.

In turn, those allies could refuse to assist the U.S. in future military operations. They could also refuse to host America’s many military bases around the world. That doesn’t make America strong. To the contrary, it weakens the U.S.’ strategic placement in the world.

Disengaging NATO, in effect, weakens American security. And if Trump continues to ignore Putin’s expansionism, Russia will be America’s problem as well as Eastern Europe’s.