Sokol, a former Berkshire Hathaway executive who resigned following a questionable investment, has also resigned from the Bruning campaign.
Bruning, who is also Nebraska's Attorney General, made the announcement as he accepted an endorsement from the national Tea Party Express in Washington.
Bruning says Sokol called within the last two weeks to offer his
resignation "in light of the circumstances."
Those circumstances include accusations from Berkshire - the
investment company run by Warren Buffett - that Sokol violated
company ethics and insider trading policies by investing roughly
$10 million in chemical company Lubrizol while he was evaluating
the chemical firm as a possible acquisition.
Last week, Buffett called Sokol's behavior inexplicable as well as inexcusable.
Sokol has denied any wrongdoing.