Nearing completion of officer training, Eidsness received a change of orders from explosive ordinance diving school to in-country Vietnam, where he served in combat in the Riverine Forces aboard USS Cohoes (AN-78) from June 1969 to June 1970, followed by duty at Naval Station Treasure Island in San Francisco Bay.
He was honorably discharged in August 1970, remained in the United States Navy Reserve, and obtained a rank of full lieutenant until his separation in 1973.
Eidsness entered federal service in the Water Quality Administration under the United States Department of the Interior in the fall of 1970, which on December 2, 1970, became the core of EPA’s Region 4 in Atlanta, Georgia.
[6] Also, he managed the first truly interdisciplinary environmental impact study on "Ocean Outfalls and Other Methods of Treated Wastewater Disposal in Southeast Florida" and completed a study at EPA Headquarters on the applicability of the National Environmental Policy Act on Transportation Control Strategies developed locally under the Federal Clean Air Act.
After two years with the international think tank, Arthur D. Little, Inc. in Cambridge, Massachusetts, where he learned the private sector trade of planning, budgeting, and managing large interdisciplinary studies, Eidsness joined the Larimer Weld Regional Council of Governments[7] as director under an EPA Section 208 clean water grant (August 1975 to July 1978).
Employers included RMT Northern Region serving primarily major manufacturing industry in the Rust Belt, Canonie Environmental Services Corp., and CH2M Hill in their Boca Raton, Orlando, and Denver Offices.
In late 2005, then-Republican Eidsness launched an exploratory committee to examine the prospect of challenging incumbent Congresswoman Marilyn Musgrave in Colorado's 4th congressional district in the 2006 Republican Primary.
Eidsness was declared the winner of a debate held in Windsor, Colorado[18] and earned the endorsement of four of six major daily newspapers, including the hometown newspapers of both his major-party opponents, the Fort Morgan Times, Musgrave’s hometown paper, and the Greeley Tribune[19] which had always endorsed Republican Candidates.