Donald Trump's selection of top hostage-affairs official Robert O'Brien as his new national security adviser sends a clear signal the president is seeking to turn the page from the confrontation and controversy that defined John Bolton's tenure in the job.

Bolton regularly picked ideological fights with Cabinet secretaries and the president over the approach to hotspots such as Afghanistan and Iraq.

O'Brien, meanwhile, is a former corporate litigator and lawyer with the military's Judge Advocate General's Corps who is seen as an ally of Secretary of State Michael Pompeo. People who know both men say O'Brien will help mediate disputes, not create them.