This month, Sgt. First Class Elis A. Barreto Ortiz and 11 other people were killed in a suicide bombing in Kabul. Mr. Trump cited Sergeant Ortiz’s death as one of the reasons he disinvited the Taliban leadership from the presidential retreat at Camp David in Maryland for talks. He later described the months of peace negotiations as “dead.”

Over the weekend, Mr. Trump tweeted that “killing 12 people, including one great American soldier, was not a good idea. There are much better ways to set up a negotiation. The Taliban knows they made a big mistake, and they have no idea how to recover!”

The death of the American Special Forces soldier on Monday came as the Taliban once again ramped up attacks across Afghanistan in the run-up to the country’s presidential elections and as the American general in charge of the command that oversees missions in Iraq and Afghanistan pledged to likely increase the pace of operations against the insurgent group.

The number of American airstrikes in the country is set to meet or possibly outpace those in 2018, and Special Operations units, alongside their Afghan counterparts, are aggressively attacking the Taliban in dozens of missions a week. Army Green Berets have made up the highest number of Americans dead this year, with eight killed in combat.

Although Mr. Trump has long said that he wanted to end the American military’s involvement in the country, it is unclear what his administration’s strategy will be in the 18-year war after the failed peace negotiations with the Taliban.