Tensions flared up in Ukraine this week when Russian naval vessels rammed a Ukrainian tugboat in the Sea of Azov on Nov. 25. The sea, over which Ukraine and Russia share navigation rights, has become a flashpoint since Russia’s annexation of Crimea in 2014. Over the last six months, Russian forces have been unlawfully detaining commercial ships seeking passage to Ukrainian ports on the Sea. The initial skirmish this past Sunday quickly escalated to Russia taking control of three Ukrainian vessels, capturing more than 20 sailors, and temporarily blocking the narrow passageway connecting the Sea of Azov to the larger Black Sea. The U.S. Ambassador to the United Nations, Nikki Haley, called Russia’s actions “an outrageous violation of sovereign Ukrainian territory.” Secretary of State Mike Pompeo condemned Moscow’s behavior and called for the immediate release of Ukrainian ships and personnel.

President Trump has not issued a statement but threatened to cancel a planned meeting with Russia’s President Vladimir Putin on the sidelines of the G-20 summit. Still, Trump has refused to hold Russia accountable for its increasingly aggressive behavior and the Kremlin confirms that the meeting will go on as planned. Ahead of the G-20, Trump’s reticence to call out Moscow for its escalatory actions sends the wrong signal to the Kremlin.

The skirmish on Ukraine’s coast is a new escalation in Russia’s four-year war with Ukraine and the latest move to destabilize Ukraine’s economy. So far, the Azov conflict seems unlikely to lead to a full scale military assault by the Kremlin. Rather, it is part of a broader Russian effort to slowly and methodically assert increasing control over Ukrainian territory—both land and sea.

In Eastern Ukraine, Russia’s creeping invasion has sparked a war killing more than 10,000 Ukrainians and displacing over 1.5 million internally. In Georgia, which Russia invaded in 2008 to lay claim on two regions, the so-called internal border keeps moving, meter by meter; slowly but surely Russia is encroaching further into Georgian territory. Frozen conflicts—as these Russian occupied regions are often called—are never truly frozen.

Moscow’s strategy is to continue to push, in this slow creep fashion, as a way to test the West’s response. If the response is weak—or mostly rhetoric without any action to back up the strong words of disapproval—the Kremlin knows that it can continue to push, acting with impunity in violation of international law, without any serious consequences. Without a red line, drawn first and foremost by the United States, Russia will be emboldened to push further into the Sea of Azov and the Black Sea, setting a dangerous precedent for China’s continued aggressive behavior in the South China Sea.

Trump’s unwillingness to confront Russia over these recent actions against Ukraine did not go unnoticed in the Kremlin. In the almost two decades that he’s been in power, Putin has shown himself to be a savvy reader of other leaders. When in 2014, Russia moved to take over and annex Crimea, the West’s weak response of limited sanctions likely emboldened the Kremlin to then invade eastern Ukraine. And when President Barack Obama did not enforce his own red line in Syria, Putin knew that there would be no retribution for Russia’s military intervention in support of Syrian dictator Bashar Assad in 2015. Putin may not be a great strategist, but he has been deft in his assessment of American leaders’ unwillingness to engage. With his continued deference to Putin, Trump is signaling to Moscow a weakness of resolve. And where Moscow sees weakness, it also sees opportunity to undermine U.S. national security interests.

If Trump wishes to engage Putin from a position of strength at the G-20, he should send a clear public message to the Kremlin that Russia’s continued violations of international law and aggression against sovereign states will be met with assertive U.S. action, whether that be tougher economic sanctions, military support for Ukraine, or increased U.S. presence in Europe’s east to shore up NATO. It is not enough for this message to come from cabinet secretaries or member of Congress. In foreign affairs, the U.S. president has the ultimate say. Trump would be wise to not repeat the errors of his predecessors by sending a message of U.S. weakness. This will only embolden Russia and others who seek to undermine the U.S. and its allies.

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