Before being sworn in as Colorado Attorney General in 2019, Weiser served in President Bill Clinton’s Department of Justice as senior counsel to the Assistant Attorney General in charge of the Antitrust Division, as a Senior Advisor for Technology and Innovation in the Obama Administration's National Economic Council, and as a Deputy Assistant Attorney General in the U.S. Department of Justice. As Deputy Assistant Attorney General in the U.S. Department of Justice Weiser worked to strengthen the review of anticompetitive mergers and led efforts to promote competition in agriculture. As Colorado’s Attorney General, Weiser has tackled crucial topics including the opioid epidemic, environmental issues, women’s rights, and criminal justice reform. He joined a multi-state lawsuit to prevent rollbacks and protect the Endangered Species Act of 1973 and protected Colorado’s land, air and water by challenging the U.S. Environmental Protection Agency’s announcement that it would roll back standards for reducing methane emissions. Weiser also filed lawsuits against opioid manufacturer Purdue Pharma and the Sackler family for their role in the opioid epidemic which affected thousands of Coloradans. Throughout the COVID-19 epidemic Weiser has been committed to preventing false COVID-19 tests from being marketed and has urged Congress to fund expanded access to the internet for basic needs such as telemedicine and online schooling.