Background: Moscow has been harassing commercial ships bound for Ukraine’s ports in the Sea of Azov for months, even though Russia and Ukraine have dual control of the sea according to a 2003 agreement. At least 150 merchant vessels have been detained since May, creating significant losses for Ukrainian ports and shipping companies.

Moscow has at least four possible motivations to escalate the conflict now:

1. Putin’s approval ratings have slipped 16 points, from 82% in April to 66% in October. In the past, the Kremlin has used foreign interventions to shore up nationalist support for Putin and secure a bump in ratings, as with the 2014 annexation of Crimea and to a lesser extent its 2015 military intervention in Syria.
2. In May, Russia opened a bridge over the Kerch Strait, connecting mainland Russia to occupied Crimea and further securing its claim to the peninsula. Moscow now seems keen to occupy the sea as well.
3. Should Russia’s Kerch Strait blockade continue, it would add pressure on Ukraine’s struggling economy. Two major Ukrainian ports — Mariupol and Berdyansk — rely on access through the strait for commercial shipments, which has already been partially restricted by the the Kerch bridge’s height.
4. Moscow may also have an opportunity to pressure President Poroshenko ahead of Ukraine's presidential elections, since he is deeply unpopular and polling in the single digits.

The bottom line: The conflict in the Sea of Azov is unlikely to lead to a massive military engagement or World War III. But the Kremlin seems confident that it will not pay a high price for low-level military aggression similar to its activities in Ukraine’s east. If the international response is weak, Moscow may see an opening for yet more assertive military strikes in the future.

Alina Polyakova is the David M. Rubenstein Fellow for Foreign Policy at the Brookings Institution.

The backdrop: Trump has made border protection the cornerstone of his domestic policy and has been raising it more often with foreign leaders as well. Last month, he criticized Germany for allowing in refugees rather than enforcing border controls and, in a call with Hungarian Prime Minister Viktor Orbán, discussed the "importance of border protection and agreed that a country that cannot defend its own borders is no longer a country."

Putin enjoys reminding others that sovereignty is at the core of his worldview. He has used “sovereignty protection” as justification for intervening in Syria on behalf of Bashar al-Assad, committing to defend Syria’s “territorial integrity” even in the face of Assad's chemical weapons attacks on his own people and the subsequent U.S.–led coalition bombing of Syrian positions.

The Russian president has also used the principle of non-interference in other countries’ domestic affairs to justify expelling Western non-governmental organizations from Russia and suppressing Russian independent media by labeling them as foreign agents. It is this same supposed commitment to the sovereignty principle that Putin uses to deny Russian meddling in foreign elections.

Alina Polyakova is the David M. Rubenstein Fellow for Foreign Policy at the Brookings Institution.

During the Cold War, the U.S. never recognized Soviet occupation of the Baltic States —Estonia, Lithuania and Latvia — a policy enshrined in the 1940 Welles Declaration, which established that the U.S. would not allow predatory behavior contrary to international law. And the U.S. government stood by this principle for five decades, until the Soviet Union collapsed in 1991. Today, the Baltic states are NATO members as well as EU and U.S. allies. In short, the nonrecognition policy kept the U.S. on the moral high ground on the basis of principles, values and commitment to international law.

If the Trump administration moves to recognize Crimea, it would mark a de facto acknowledgment that international laws are obsolete; that other states have the right to take territories by force; and that U.S. sanctions tied to Russian occupation of Crimea are irrelevant. This would establish a dangerous precedent. No doubt, China would take such a move as a sign that it can ramp up its expansion into the South China Sea without much consequence.

The bottom line: In opening the door to a policy change on Crimea, the U.S. would give up significant leverage over Russia, a country the administration has called a U.S. adversary. The U.S. should seek to negotiate from a position of strength with Putin — changing course on Crimea would only achieve the opposite.

Alina Polyakova is the David M. Rubenstein Fellow for Foreign Policy at the Brookings Institution.