Two years ago, just six days after the Russian invasion of Ukraine, President Biden opened his State of the Union address by vowing to stop Vladimir V. Putin in his tracks. The response in the House chamber was a series of standing ovations.On Thursday night Mr. Biden again opened his address by repeating his warning that, if not stopped, Mr. Putin would not halt his territorial ambitions at Ukraine’s borders. But the political environment was completely different.With many Republicans vowing not to vote for more aid and Ukrainians running short of ammunition and losing ground, Mr. Biden…