Scott Colom is Mississippi’s senator-elect after he toppled Republican incumbent Cindy Hyde-Smith. Few people paid attention to his campaign at first, but he kept working hard. His win surprised many, as the state had not elected a Democratic senator since the 1980s. He now heads to Washington to start work.

Few were paying much attention to Scott Colom for most of his campaign. Then he toppled the Republican incumbent.

Barely more than a year ago, Scott Colom sat at the kitchen table at his parents' house not far from his own home in northeastern Mississippi, using his lunch breaks from his job as district attorney to call potential donors.

Mississippi hadn't had a Democratic senator since the 1980s. It hadn't had a Black senator since the 1880s. But Mr. Colom made his pitch.

The response, in the recollection of his mother, Dorothy Colom, was typically a one-two beat:

You sound impressive.

You can't win.

"It was just the two of us," she said in an interview this week at her home in Columbus, Miss. "And my role was just to write down what the donors said."

Now Mr. Colom, 43, is Mississippi's senator-elect -- and at the top of the list of Democrats whose unlikely wins in the midterm elections reordered the balance of power in Washington and scrambled longstanding preconceptions about who can win where.

A seventh-generation Mississippian descended from an enslaved woman, Mr. Colom (pronounced kuh-LOAM) defeated Cindy Hyde-Smith -- the Republican incumbent who had single-handedly denied him a chance at a lifetime appointment as a federal judge three years before, blocking his nomination by President Joseph R. Biden Jr.