Ms. Gross, a coordinator of faith development at a Catholic college in Dubuque, said that she had attended rallies for Mr. Buttigieg on Saturday and for Mr. Biden earlier on Sunday.

“I thought both were good but I cried today — I mean when I heard Joe, it was so beautiful,” she said.

She was torn up by his description of grade-school children participating in active shooter drills, something a granddaughter of hers had gone through.

Her husband, Terry, announced that he had finally decided to back the former vice president.

“The Democrats sometimes don't express their faith, and Joe is a man of faith — I can tell,” he said. “He said, ‘I went to church this morning.’ That says a lot to me.”

Ms. Hermsen stood beside a refrigerator covered with family pictures, including of her two sons, both engineers. “I think I’m leaning toward Biden,” she said.

“We just really had a good experience with him today,” Ms. Gross told her. “He was amazing. You would have been crying. So powerful.”

“I want someone experienced,” Ms. Hermsen, a kindergarten teacher, replied. “Do I want to go to a doctor that’s new? No. I want someone who knows what they’re doing. So it’s like, why would I not want someone experienced in the White House?”