The buildup of Russian troops near Ukraine has left U.S. officials perplexed, muddying the Biden administration’s response. Some Republican lawmakers have been pressing the U.S. to step up military support for Ukraine. But that risks turning what may be mere muscle-flexing by Russian President Vladimir Putin into a full-blown confrontation that only adds to the peril for Ukraine and could trigger an energy crisis in Europe. But a weak U.S. response carries its own risks. […]