The winner of the GOP primary is expected to face Kerrey, a popular former governor and senator who initially opted out of running for retiring Sen. Ben Nelson's (D-Neb.) seat, but changed his mind last week.

Another poll released Tuesday by Rasmussen, a GOP polling firm, showed all three Republicans in the primary — Stenberg, Bruning and state Sen. Deb FischerDebra (Deb) Strobel FischerSenate approves Trump's debt deal with Democrats Trump administration turns to rural communities for input on infrastructure bill Senators eye ticket fee to overhaul airports MORE — beating Kerrey by double digits in a general election. In the case of Bruning, the Republican lead was 22 points over Kerrey.

The Rasmussen poll of 500 likely voters was conducted March 5 and had a margin of error of plus or minus 4.5 percentage points.