A poll released by Missouri Senate candidate John Brunner showed him up by 20 points over his competitors in the GOP primary.

In a horse race matchup among likely primary voters, Brunner led with 40 percent, followed by former state Treasurer Sarah Steelman and Rep. Todd Akin with 20 percent each. Nineteen percent of respondents were undecided.

A spokesman for the Brunner campaign said it was a clean ballot test — that is, respondents weren’t given any additional information before being asked their candidate preference.

Among those aware of all three candidates, Brunner, a businessman, led 44 percent to Akin’s 22 percent and Steelman’s 18 percent.

The poll was conducted by Linda DiVall and Randall Gutermuth of GOP polling firm American Viewpoint, Inc. Using live telephone interviewers, the poll surveyed 600 likely Missouri GOP primary voters on landlines and cellphones from June 19-21. The margin of error was 4 points.

The winner of the Aug. 7 Republican primary will take on vulnerable Sen. Claire McCaskill (D) in November.

Roll Call rates the Missouri Senate race as a Tossup.

Here’s the polling memo:

[scribd id=98206563 key=key-1u6heuyx0c9dj9vc1v3n mode=list]