Robert Harward Turns Down Trump's National Security Adviser Offer
Retired Vice-Admiral Robert Harward was widely tipped for the post after Mr Trump fired Michael Flynn on Monday.
A White House official said Mr Harward cited family and financial commitments, but US media said the sticking point was he wanted to bring in his own team.
Mr Flynn had misled US Vice-President Mike Pence over his conversations with Russia's ambassador to the US.
The latest setback emerged hours after Mr Trump robustly denied media reports of White House disarray, insisting in a news conference that his administration was running like a "fine-tuned machine".
The White House is expected to name its new communications director on Friday, and US media say the job will go to Mike Dubke, the founder of Republican media group Crossroads Media.
Mr Harward told the Associated Press the Trump administration was "very accommodating to my needs, both professionally and personally".
"It's purely a personal issue," added the 60-year-old former Navy Seal who is currently based in Abu Dhabi as an executive for US defence contractor Lockheed Martin.