Take this for what its worth but Gemini responded with this.

Assessing which U.S. president is responsible for the most civilian deaths depends heavily on how one defines "presidential action."

If the definition includes initiating full-scale wars (invasions/occupations), the highest death toll occurred under George W. Bush due to the Iraq War.

If the definition focuses on direct airstrikes and drone warfare (specific targeted operations), available data suggests the rate and intensity of civilian casualties were highest under Donald Trump, who relaxed rules of engagement and intensified bombing campaigns against ISIS.

Here is a detailed breakdown by administration.

1. George W. Bush (2001–2009)1. George W. Bush (2001–2009)

Primary Driver of Casualties: Full-scale invasion and occupation (Afghanistan and Iraq).

• Scale: The decision to invade Iraq in 2003 resulted in the highest overall loss of civilian life among the three presidencies.
• Casualty Estimates: The Costs of War Project (Brown University) estimates that over 180,000 to 200,000+ civilians died directly from violence in the Iraq War alone. While not all were killed directly by U.S. forces (many died in the resulting sectarian violence and insurgency), the invasion is the "presidential action" that precipitated these deaths.
• Direct U.S. Fire: During the "Shock and Awe" invasion phase and subsequent occupation, thousands of civilians were killed directly by coalition airstrikes and ground forces.

2. Donald Trump (2017–2021)2. Donald Trump (2017–2021)

Primary Driver of Casualties: Intensified airstrikes, relaxed rules of engagement, and the siege of ISIS strongholds (Mosul and Raqqa).

• Rate of Killing: Independent monitors like Airwars reported that civilian deaths in Iraq and Syria skyrocketed under Trump. In his first six months, the U.S.-led coalition reportedly killed more civilians than were killed during the entire three years of the anti-ISIS campaign under Obama.
• Policy Changes: Trump delegated more authority to field commanders and revoked an Obama-era requirement (via executive order) that required the director of national intelligence to publish an annual report on civilian deaths outside active war zones.
• Specific Theaters: Drone strikes and raids also increased in Yemen and Somalia. In 2017, U.S. strikes in Yemen reportedly tripled compared to 2016.

3. Barack Obama (2009–2017)3. Barack Obama (2009–2017)

Primary Driver of Casualties: Expansion of the drone program and troop surges in Afghanistan.

• Drone Warfare: Obama vastly expanded the use of drone strikes compared to Bush (authorizing over 500 strikes compared to Bush's ~50).
• Casualty Estimates: While Obama normalized the use of targeted killing, independent organizations (like the Bureau of Investigative Journalism) estimate civilian deaths from his drone strikes in the hundreds (approx. 300–800+ outside active war zones), which is significantly lower than the casualties resulting from the ground wars under Bush or the carpet-bombing tactics used against ISIS under Trump.
• Transparency: Toward the end of his presidency, he instituted policies requiring the reporting of civilian casualty numbers, though critics argued these official numbers often undercounted deaths compared to independent reports.

Summary ComparisonSummary Comparison

ConclusionConclusion

• If you count total deaths from wars started, George W. Bush has the highest toll.
• If you count deaths per month from direct U.S. airstrikes, Donald Trump oversaw the deadliest periods.

I’m pretty confident that Trump is the low water mark for the 21st century. It might depend how Covid ends up getting scored though.