"They have been reduced to a point where it's embarrassing for our country," he said. "I can just see the great, as an example, General George Patton spinning in his grave — as we can't beat ISIS.
"I have great faith in the military," he continued. "I have great faith in the commanders certainly.
"But I have no faith in Hillary Clinton or the leadership."
He said that he did have a plan to defeat ISIS, despite saying in a speech in Philadelphia that he would ask military leaders to develop a program within 30 days after he became president.
"I have a substantial chance of winning," he told Lauer. "If I win, I don't want to broadcast to the enemy exactly what my plan is.
"If I like — maybe a combination of my plan or the generals' plan, if I like their plan."
Regarding Russian President Vladimir Putin, Trump said that "the man has very strong control over a country.
"It's a very different system — and I don't happen to like the system, but certainly in that system, he's been a leader," he added. "Far more than our president has been a leader."
Trump added that "I think I would have a very good relationship with many foreign leaders.
"The beautiful part of getting along, Russia wants to defeat ISIS as badly as we do," he continued. "If we had a relationship with Russia, wouldn't it be wonderful if we could work on it together and knock the hell out of ISIS?
"Wouldn't that be a wonderful thing?"
When Lauer noted that Putin has praised Trump, he responded, "the fact that he calls me brilliant or whatever he calls me is going to have zero impact."
In response to a veteran's question about sexual assault in the military, Trump pledged that "we'll run it right.
"I want to keep the court system within the military. It shouldn't be outside of the military. We have to come down very, very hard on that.
"The best thing we can do is set up a court system within the military," he added. "Right now, the court system practically doesn't exist. Takes too long."