Trump has since named Ret. Lt. Gen. Joseph Keith Kellogg, who worked under Flynn until the latter was asked to resign, as the acting national security adviser. Asked if there was a candidate for national security adviser in sight, a White House official told CNN, "Not that I'm aware of."
"Since retiring, I have the opportunity to address financial and family issues that would have been challenging in this position," Harward said in a statement. "Like all service members understand, and live, this job requires 24 hours a day, 7 days a week focus and commitment to do it right. I currently could not make that commitment. My thoughts and prayers are with those that carry such heavy burdens and responsibility for taking care of our country's national security concerns. God bless this great country of ours."
A friend of Harward's said he was reluctant to take the job because the White House seems so chaotic. Harward called the offer a "s*** sandwich," the friend said.
A Republican official told CNN that Harward made it a condition of taking the job that he could form his own team. In the end, he didn't feel that was the case.
And a senior Republican familiar with the process added that "a question of clarity regarding the lines of authority" was central in Harward's decision.
"I wouldn't call it a disagreement as much as questions that could not be resolved to his comfort level," the senior Republican said.
White House chief of staff Reince Priebus told Fox News on Friday the administration "told Adm. Harward that we were very interested in talking to him, and we were very serious about his position at the NSA."
"He responded, 'well, let me talk to my wife and family, and we'll get back to you.' And we kept in constant contact," Priebus said. "He called us and said guess what? I've got some support in the family but others aren't that excited about it. And he then told us that it was something that his family couldn't go for. But he was honored to be talked to, and it wasn't going to happen. It was a reasonable thing."
Harward served as Mattis's deputy when he was commander of US Central Command, which oversees US military operations in Iraq and Afghanistan.
Flynn was forced to resign his position in the Trump administration after reports said he discussed sanctions with the Russian ambassador before Trump was inaugurated and misled Vice President Mike Pence about the conversation. The White House said Flynn's omission about the details of his conversation led to an erosion of trust between Flynn and the President, prompting Flynn's exit.
Following a more than 30-year military career, Harward became chief executive of defense giant Lockheed Martin's United Arab Emirates division.
Harward was already familiar with the role of national security adviser and the work of the National Security Council, having previously worked on the NSC's counterterrorism office from 2003 to 2005 during President George W. Bush's administration.
After Flynn's resignation, Harward's name floated to the top of lists for potential replacements, alongside acting adviser Kellogg and retired Army Gen. David Petraeus, who pleaded guilty in 2015 to mishandling classified information after he shared sensitive material with a woman with whom he was having an affair.
Ret. Army Maj. Gen. James "Spider" Marks, a CNN military analyst, called Harward an "incredibly talented guy" in an interview with CNN's Erin Burnett on "OutFront.
Marks said he didn't want to speculate why Harward turned down the job, but said turmoil in the White House was likely a contributing factor.
"I'm sure Bob looked at this, Adm. Harward looked at this, and said, 'Look there's a lot of forming and storming going on right now.'"
But Sen. James Lankford, R-Oklahoma, dismissed suggestions that White House chaos led to Harward's decision to not accept the role, calling it "hearsay."
"Am I surprised, 72 hours after Flynn resigns, that we're still in the process of doing a turn for that? No, I'm not," he told Burnett.
A senior administration official insisted Friday that the White House isn't having trouble filling the role. The official said the administration is making a final decision and is talking to a few other people, saying there are one to two others beyond Kellogg and Petraeus who are in the mix.
When asked why the administration won't just name Kellogg, the official responded "there's everything right with Kellogg."
"We're just making sure that when we pull the trigger and finally pick the person that we have the proper diversity of choice before the President then makes his decision," the official said.