Jamie Dettmer is opinion editor and a foreign affairs columnist at POLITICO Europe. This winter is shaping up to be the most hazardous of the war for Ukraine — at least since the early months of the invasion nearly four years ago, when Russia’s armored columns were closing in on Kyiv.  Back then, doughty Ukrainian resistance, the 2,000 anti-tank missiles Britain supplied just weeks before the invasion and Russian tactical incompetence saved the day — along with President Volodymyr Zelenskyy’s