The Ukrainian ships were well within their rights to be there - a similar group of ships went through the strait just a month ago, and a 2003 treaty guarantees the rights of both nations to use those waters. But this time, in a carefully arranged provocation, Russian ships fired on the Ukrainian ships - and then seized them, along with 23 crew members.
In a certain sense, these events are no surprise. Though many have found it convenient to forget, the war between Russia and Ukraine still rumbles on. Those who are doing the fighting have long been braced for a Russian acceleration of the conflict. The only surprise is the timing: Why now?
Maybe there is no special reason. There have been a number of clashes in the waters around Crimea recently, ever since the Russians built a bridge to the peninsula; this may simply be Russia's periodic reminder that it will not end its illegal occupation. The attack on the Ukrainian navy would also fit well into a bigger regional project: the long-term pressure on the port of Mariupol as well as a long stretch of Ukrainian coast that could be cut off from the rest of the Black Sea by the closure of the Kerch Strait.
But this is also an interesting moment in Russian domestic politics. This little military escapade comes in the wake of wide protests against changes to Russian pension laws, and is accompanied by wide frustration with the slow economy.
As news of what was described, of course, as a Ukrainian provocation broke in Russia, the country's most prominent opposition activist, Alexei Navalny, immediately observed that recent polls showed a drop in the popularity of Russian President Vladimir Putin. Expect to hear more on television, he wrote sarcastically, about the "aggressive Kiev military, supported by hawks from the Potomac."
The timing might also have been chosen with an eye to the political calendar in Ukraine, which is gearing up for a presidential election next March. Perhaps the Russians want to inject a polarizing element into an already divided society; perhaps this is an answer to the Ukrainian Orthodox Church's decision to break away from Russia; perhaps they want to provoke a postponement of the election altogether. In a narrow sense, they may already have succeeded in changing the political atmosphere.
At a late-night meeting Sunday, President Petro Poroshenko - now far behind in the polls - called for a period of martial law in part of the country, and parliament voted Monday to impose it. It's not clear yet what this means. It seems just to include military mobilization - Poroshenko has said there will be no restrictions on media or public gatherings, and no postponement of the election - but accusations of election meddling are already flying.
Finally, the timing may be linked to international politics. Britain, one of the countries that has been most adamant about sanctions on Russia, is right now turning inward for a monumental battle over its withdrawal from the European Union; there isn't much political bandwidth in London to worry about Ukraine. President Donald Trump's administration is divided, distracted and preparing to contend with Democrats in the upcoming House majority who will, among other things, investigate his past ties to Russia.
The EU, Canada and even Poland came out with official statements condemning the Russian actions long before anything was heard from the United States. On Monday evening Kiev time, the State Department had still not reacted to the events in the Kerch Strait. U.N. Ambassador Nikki Haley's denunciation of Russia's "outlaw actions" came many hours after the other statements.
Whatever the other motives for this staged attack, this kind of passivity may well be what the Russians are counting on. This is the modus operandi they have followed in the past: Take a few steps forward; wait for a reaction. If there isn't one, move farther. If there is one, wait for the emotions to die down - and then move farther.
This incident may or may not end here, but consider it a warning: If we don't have a broader strategy for ending this war, that will be the pattern for years to come.