Sen Bennett came third at a Republican Party convention in Salt Lake City.
The two challengers, one backed by the Tea Party, will face each other in a primary next month for the right to contest November’s Midterm elections.
It is the first major victory for the grassroots movement that objects to big government and opposes high spending.
Sen Bennett was criticised by Tea Party activists for supporting the Wall Street bail-out, co-sponsoring a bipartisan bill mandating health insurance coverage and aggressively seeking funding “earmarks” for his state.
“The political atmosphere obviously has been toxic and it’s very clear that some of the votes that I have cast have added to the toxic environment,” he told reporters after Saturday’s convention vote.
Mili Note: Bye bye, Bob. So much for your Senator-for-Life position. Now it’s Orrin’s turn!