Retiring Sen. Ben Nelson (D-Neb.) will not endorse former Sen. Bob Kerrey (D-Neb.) in a Democratic primary.

"I usually don't take sides in contested primaries, so that's pretty much where I am," he told The Hill on Tuesday.

Kerrey has long been national Democrats' preferred choice, but after he initially said he wouldn't run, Nebraska Regent Chuck Hassebrook (D) entered the race.