Hillary Clinton campaign manager Robby Mook stumbled Wednesday when pressed on how the Democratic presidential nominee's policy on Syria would differ from that of the current administration.

Mike Barnicle and Willie Geist grilled Mook on MSNBC's "Morning Joe" about what Clinton would do about the Syrian civil war, which has dragged on for five years with no end in sight.

Toward the end of the questioning, host Joe Scarborough jumped in and confronted Mook, saying, "We love you, buddy, but what are you here for if you can't answer basic questions?"

It started with Mook seeming unwilling to answer policy questions posed by Geist and Barnicle.

"Hillary Clinton was secretary of state when this crisis began," Geist said. "What's her biggest regret about the way Syria's been handled?"

Clinton served as secretary of state under Obama from 2009 until 2013, and Mook pointed out that she wasn't in office when the Syrian crisis accelerated. Geist then noted that she was, however, serving in that role when the conflict started in 2011.

"Well, right, but, you know, yeah. She — I think she's well regarded for her leadership as secretary of state," Mook said. "She came out of that office with a 70% approval rating."

Mook then pivoted to attack Donald Trump, the Republican presidential nominee.

"She in contrast to Donald Trump has released a clear and decisive plan to defeat ISIS," Mook said. "Donald Trump has said that he thinks he knows more about it than the generals and refuses to tell us what his secret plan is."

Geist continued pressing him.

"What about in Syria, though? She supported the drawing of the red line," Geist said, referring to a "red line" from the Obama administration stipulating that the US would intervene if the regime of Syrian President Bashar Assad used chemical weapons against civilians.

Geist asked: "Obviously she was out of her office when Assad used chemical weapons. Was it a mistake to draw the red line if the president was not willing to do something about it when it was crossed?"

Mook again dodged.

"Well, as you pointed out, the decision regarding that was made after she was out of office, so I think you'd have to ask President Obama," he said.

Geist then asked whether Clinton was disappointed in the handling of the red-line issue. Obama declined to strike Assad after evidence of the chemical weapons attack emerged, instead brokering a deal with Russia for the removal of the regime's arsenal of chemical weapons.

"I think you'd have to ask her about that question, how she would characterize it," Mook said.

Geist pointed out that Mook was "here to speak for" Clinton. But Mook again changed the subject to attack Trump.

"Look, what matters is what she is going to do as president," Mook said. "As I said, she has a clear plan to defeat ISIS. Donald Trump does not. It's a secret. He won't tell anybody what it is and he says he knows more than the generals. I think the choice is clear."

Barnicle later jumped in to press Mook further.

"So, Robby, we do realize that you are not secretary of state, but in the debate next Monday evening how would Secretary Clinton respond to somewhat of a version of the following question, we've had a relief convoy bombed, potentially a war crime, leading into Aleppo," Barnicle said.

"What would you do, Secretary Clinton, about providing food, water, and medicine to the citizens of eastern Aleppo today, right now, differently than what the Obama administration is doing?"

But Mook again demurred.

"Again, I think you're going to have to ask her that question," Mook said. "That's a matter of policy, and I'm going to leave it for her."

That's when Scarborough jumped in.

"We love you, buddy, but what are you here for if you can't answer basic questions?" Scarborough said.

"I mean, I don't know if there's a — I mean, we may be tiptoeing into Gary Johnson territory here if you don't know the answer to that basic of a question," he said, referring to the Libertarian presidential nominee's seeming caught off guard when asked about the crisis in Aleppo in an interview. "What is the response to Aleppo? Then why do we have you here?"

Mook stuck to his line.

"I think — look, you're asking new policy questions," he said. "You would have to ask the secretary."

Scarborough didn't back down.

"New? Aleppo's been around for — Syria's been around for some time," he said. "The red line being drawn has been around for some time. I'm not being difficult here at all — these are basic questions."

Mook stood his ground as well.

"I'm not being difficult either," he said. "I'm simply saying that she has laid out a plan to defeat ISIS, and if there are new questions pertaining to Aleppo, I'm going to need to let her answer those, and she will answer those in the debate, and we look forward to her having the opportunity to do that."