Democrats need four seats to win a majority — but very few Republican incumbents look beatable right now. Susan Collins, who sits atop the list, is fairly popular in Maine.

The other two most vulnerable Republicans are Sens. Cory Gardner of Colorado and Martha McSally of Arizona, who’s being challenged by Mark Kelly, the retired astronaut turned gun-control advocate.

But even if Democrats somehow took out those three, they’ll still struggle to hold onto the seat of Sen. Doug Jones in deep-red Alabama.

Many Democrats wish these 2020 presidential candidates — and possibilities — would run for Senate instead: Beto O’Rourke in Texas, John Hickenlooper in Colorado and Steve Bullock in Montana.