Federal prosecutors could soon bring criminal charges against former national security adviser John Bolton, marking a dramatic escalation in a yearslong investigation into one of President Donald Trump’s most outspoken Republican critics.

Bolton, who served as Trump’s national security adviser until 2019, had his Maryland home and Washington, D.C. office searched by law enforcement in August as part of a national security investigation led by the U.S. attorney’s office. The investigation traces back to the final months of Trump’s first term and continued under the Biden administration, a key detail that could weaken claims of political bias amid Democrats critical of recent indictments targeting Trump adversaries.