DENVER — Republican presidential nominee Donald Trump on Friday called retired Marine Gen. John Allen a “failed general” after the highly respected military veteran delivered a forceful endorsement of Trump’s opponent, Hillary Clinton, earlier this week.

“They had a general named John Allen, and he – I never met him,” Trump said during a campaign rally. “And he got up and he started talking about Trump, Trump, Trump. Never met him. And you know who he is? He’s a failed general.”

Allen is a retired four-star general who served as commander of the International Security Assistance Force in Afghanistan. He was President Barack Obama’s top choice to oversee U.S. and NATO operations in Europe, but instead he retired to assist his wife with chronic health issues. He came out of retirement in 2014 when the president named him Special Presidential Envoy for the Global Coalition to Counter the Islamic State in 2014, a position he held for a year.

“He was the general fighting ISIS. I would say he hasn’t done so well, right? Not so well,” Trump added, referring to the Islamic State terrorist group.

Trump has regularly faulted the foreign policy establishment for failing to contain the Islamic State. He has also dismissed foreign policy experts on the campaign trail, particularly those who have criticized him, knocking their failure to produce solutions to ongoing ethnic and religious conflicts in the Middle East.

Trump’s pitch to supporters on foreign policy rests on his “America First” motto, which has vacillated between contradictory promises to “bomb the (expletive) out of ISIS” and calls for a contracted American presence abroad.

Allen indirectly attacked Trump during a speech Thursday at the Democratic National Convention, assailing the Republican candidate’s support for waterboarding, for which Trump has regularly spoken in favor. Allen also criticized Trump’s approach to international relations.

“With her as our commander in chief, our international relations will not be reduced to a business transaction,” Allen said, speaking to Clinton’s foreign policy credentials. “I also know that our armed forces will not become an instrument of torture, and they will not be engaged in murder or carry out other illegal activities.”

Trump’s attack Friday evening capped a day-long tirade against Clinton and several individuals who spoke at the Democratic National Convention this week.

He also criticized Allen on Twitter Friday morning: “General John Allen, who I never met but spoke against me last night, failed badly in his fight against ISIS. His record = BAD #NeverHillary.”