Neumann served during the George W. Bush administration managing President Bush's Faith-Based and Community Initiatives, which involved working with the Departments of Education and Housing Development. From 2003 to 2005, Neumann worked at the White House as part of the inaugural staff of the Homeland Security Council post 9/11, where she worked with government security agencies to counter terrorism. Newmann was part of a team of officials that enacted several anti-terrorism measures. Neumann served as an executive assistant to Homeland Security Advisor, John A. Gordon, and eventually became a Homeland Security policy advisor and later Associate Director of the Domestic Counterterrorism Directorate. As Associate Director, she advised the presidential appointee on Homeland Security policy initiatives. Neumann left the Bush administration and worked with the Senior Advisor to the Program Manager for the Information Sharing Environment, Office of the Director of National Intelligence, where she helped author and coordinate the implementation of key components of the 2007 White House National Strategy for Information Sharing. She also worked as a contractor assisting businesses with cyber security and risk assessments and helped the Department of Homeland Security (DHS) develop threat assessments and restructure and open regional field offices.

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Neumann joined DHS Secretary John Kelly as his Deputy Chief of Staff in 2017, and she served in the same capacity under Acting DHS Secretary Elaine Duke. In 2018, Neumann transitioned into her role as DHS Assistant Secretary for Threat Prevention and Security Policy, where she served until her resignation in April 2020. In that capacity, she was in charge of emerging threats — and had identified violence perpetrated by right-wing extremists as a major threat. Neumann pushed the department to do more to prevent domestic terror attacks; and worked with bipartisan support in Congress to get new funding that helped bolster and rebrand the Countering Violent Extremism Task Force into the Office of Targeted Violence and Terrorism Prevention (TVTP) within DHS. She testified before Congress that DHS saw extremism building to the 'doorstep' of another 9/11.