DES MOINES, Iowa — Iowa Democrats on Monday are kicking off the 2020 presidential nominating race at the first-in-the-nation caucuses, but many are dogged by fears that they will make the wrong pick. They universally agreed that they must oust President Trump in November but they tie themselves in knots about how to do it. Was it the “safe” choice in Joe Biden? A liberal hero in Sen. Bernard Sanders of Vermont or Sen. Elizabeth Warren of Massachusetts? A youthful moderate such as former South Bend, Indiana, Mayor Pete Buttigieg or Sen. Amy Klobuchar of Minnesota? The president, it seemed,...