It’s easy to imagine the Democrats losing the Senate:
1. Very good chance: Republicans hold all their current seats.
2. Very strong chance: Republicans pick up Colorado, Nevada, North Dakota, Arkansas, Delaware, Pennsylvania.
3. Good chance: Republicans pick up Illinois and Indiana.
4. Reasonable possiblity: Republicans pick up two from California, Wisconsin, New York or Washington.
If the cards fall right, they have 51 seats.