Former Trump campaign manager Corey Lewandowski told "Fox News Sunday" that President Trump's staffers are failing him, and he pointedly refused to say whether Chief of Staff John Kelly had grabbed him during a reportedly heated argument in the White House.

Lewandowski and former Trump deputy campaign manager David N. Bossie are the authors of the book “Trump’s Enemies: How the Deep State Is Undermining the Presidency,” which will be released on Tuesday. Both sat for an interview with Fox News' Chris Wallace on Sunday, and charged that dysfunction was evident at the White House even as they wrote the book.

"The management style that John implemented when he became the chief of staff was one where to limit the access to the president, to make sure that there are protocols and procedures," Lewandowski said. "Candidly, that was needed when he came into the White House. But I also think you have a president who wants access to individuals who wants to take phone calls. And in our book we interview him and he says, 'Nobody calls me; I don’t get my messages.'"

Other high-profile authors have reported similar challenges as they wrote deep-dives into the White House. In September, The Washington Post released an audio recording of journalist Bob Woodward's conversation with Trump on YouTube. According to a transcription of the call, Woodward told Trump he regretted that the two had not been able to sit for an interview in advance of Woodward's book "Fear," which portrayed the White House as chaotic and poorly managed.

"Well, I just spoke with Kellyanne [Conway] and she asked me if I got a call," Trump tells Woodward, referring to his senior adviser and longtime confidante. "I never got a call. I never got a message. Who did you ask about speaking to me?" During the call, Conway apparently walks into the room with Trump, and the president asks her directly, "Why didn't you tell me?"

"It’s really too bad, because nobody told me about it, and I would’ve loved to have spoken to you," Trump explains.

Lewandowski told Wallace that something needs to be done about the apparently persistent problem.

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"That is a failure somewhere in the staff chain -- that the president doesn’t have the right to get to the people who are trying to reach him, and I don’t know where that failure is but ultimately that should be resolved," he said.

The relationship between Kelly and Lewandowski has publicly deteriorated for months. In an article last month that cited a "half-dozen people familiar with the events," The New York Times reported that Kelly had grabbed Lewandowski “by the collar” during an argument in February just outside the Oval Office, reportedly necessitating an intervention by the Secret Service. The altercation involved Kelly shoving Lewandowski into a wall after he criticized Kelly's handling of domestic violence accusations against a former White House staffer, the Times reported.

Former White House Communications Director Anthony Scaramucci told Fox News' "Fox & Friends" he was "very confident" that the incident occurred, and Lewandowski told Fox News' "The Ingraham Angle" in October that "What may or may not have taken place, ten months ago, eight months ago, is completely irrelevant to where we are today."

On Sunday, Lewandowski denied details of the purportedly tense encounter -- but only to a point.

"Well the Secret Service didn’t break anything up," Lewandowski said. "John and I had a very candid discussion, as he probably has many times with the president."

Asked directly by Wallace if Kelly had grabbed him, Lewandowski replied, "I don’t want to get into what John may have or may have not done, but what I do think is he understands that my position is to support the president and the president’s agenda all the time."

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Kelly has previously been reported to take an aggressive approach in other circumstances. In October, The Wall Street Journal reported that during Trump's visit to China last year, Kelly and Secret Service agents "got into a physical altercation" with a Chinese official who sought unauthorized access to the highly-secured nuclear football, the nearly 50-pound briefcase that allows the president to launch nuclear missiles remotely. The paper reported that Kelly would only accept an apology if a Chinese official made it in Washington while standing under a U.S. flag.

Axios reported that a Secret Service agent tackled a Chinese official after a military aide carrying the football was denied entry into a room with the president. When Kelly became involved, according to the report, he was grabbed by a Chinese official, prompting the Secret Service to protect him.

And multiple outlets reported last month that Kelly had gotten into a protracted shouting match with national security adviser John Bolton.

"I don’t want to get into what John may have or may have not done." — Corey Lewandowski

Trump definitively told Wallace in an exclusive interview last week that Kelly will "move on" at some point, even as he claimed there was still some chance Kelly will stay with the administration through 2020.

"There are certain things; I love what he does," the president said. "And there are certain things that I don’t like that he does -- that aren’t his strength. It’s not that he doesn’t do -- you know he works so hard. He’s doing an excellent job in many ways. There are a couple of things where it’s just not his strength. It’s not his fault, it’s not his strength. ... But John, at some point, is going to want to move on. John will move on."

Separately, Lewandowski took aim at what he called misconduct by intelligence officials bent on targeting Trump.

"A big part of what we outline in this book is how the intelligence community went after the president through the FISA application process and those individuals who ran the campaign because they simply disagree with his political philosophy and that should be a very scary thing for every American," he said.

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Lewandowski also told Wallace that the midterm elections -- which saw Democrats retake the House and make significant gains in state legislatures and governor's mansions -- weren't necessarily a discouraging sign for Trump. Last week, incumbent Republican Utah Rep. Mia Love, whom Trump derided in a post-Election Day news conference for failing to embrace him, was narrowly defeated by Democrat Ben McAdams in a race that took two weeks to settle.

"The individuals who were running in some of these places ran away from the president, which I think was a mistake, particularly in some of those House seats," he said. "When you look at where the president campaigned the most, whether it was Georgia or Indiana or in Florida, those candidates were winning time and time again because the Republicans and the Independents came out and supported those candidates, which I think by extension was the Trump agenda."

Bossie predicted that continued strong economic numbers will probably carry Trump to victory in 2020.

"One of the great things he’s done as president is educate the American people about what’s going on in fake news," Bossie said. "And I think he is going up against – you talk about that map – he’s going up against the entire establishment of the Washington Democratic Party and the media. He has a big hill to climb, and he is going to do it because he is going to tell the American people about his incredible list of accomplishments and where our economy is."