On Monday, an explosion ripped up a section of road across the Kerch Strait bridge, Putin’s pet project linking the Russian mainland with illegally annexed Crimea. It was the second time the bridge was hit in less than a year. The last time, in October, a truck bomb ruined part of the rail lines. This time, the damage was the work of naval drones. Vladimir Putin promised retribution and he quickly delivered: He pulled Russia out of the expiring grain deal that allowed Ukrainian agricultural products to leave the ports Russia has blockaded, and then attacked those ports—Odesa and Mykolaiv—destroying a massive fuel depot. The attack, his spokesman confirmed, was revenge.

Though Ukraine hasn’t officially taken responsibility, the attack on the Kerch bridge is part of the deep war that the country has been waging on Russian supply lines. About a month ago, Ukraine punctured another Russian-controlled bridge, across the straits of Chonhar, this time with a British Storm Shadow missile. Unlike the Kerch bridge, which was designed to square a geographic circle—Crimea isn’t actually attached to Russia by land—the Chonhar bridge was the shortest possible route from Crimea to the fronts in Kherson and Zaporizhzhia. It was also similar to Ukrainian missile strikes deep into Russian-occupied territory targeting major ammunition depots. A strike last week, on the occupied seaside town of Berdyansk, killed a Russian lieutenant general, the deputy commander of Russia’s southern military district.