WASHINGTON — With enthusiasm fading for Ukraine aid, a pair of Texans have been raising alarms about complacency in the face of Russian aggression. Sen. John Cornyn and the House Foreign Affairs chairman, Austin Rep. Michael McCaul, have both evoked Britain’s missed opportunity to confront Nazi Germany before World War II. Both have been trying to tamp down growing impatience among fellow Republicans by reminding them that Ukraine is a buffer preventing a direct and catastrophic clash between Russia and the United States. “We have to educate our members. I don’t think they quite understand what’s at stake,” McCaul said...