President Trump appointed Lt. Gen. H. R. McMaster as his new national security adviser on Monday, picking a widely respected military strategist known for challenging conventional thinking and helping to turn around the Iraq war in its darkest days.Mr. Trump made the announcement at his Mar-a-Lago resort, where he interviewed candidates over the holiday weekend to replace Michael T. Flynn, who was forced out after withholding information from Vice President Mike Pence about a call with Russia’s ambassador.Unlike Mr. Flynn, who served as a campaign adviser last year, General McMaster has no links to Mr. Trump and is not thought of as being as ideological as the man he will replace. A battle-tested veteran of both the gulf war and the second Iraq war, General McMaster is considered one of the military’s most independent-minded officers, sometimes at a cost to his own career.The selection encouraged Republicans who admire General McMaster and waged a behind-the-scenes campaign to persuade Mr. Trump to select him. Senator Tom Cotton of Arkansas, an Army veteran who once served under General McMaster, contacted the White House to suggest that it consider him, and a coterie of other national security conservatives, including a top aide to Senator John McCain of Arizona, also lobbied for him. Defense Secretary Jim Mattis, who has worked with General McMaster, encouraged him to take the job.“He’s a man of tremendous talent and tremendous experience,” Mr. Trump told reporters as General McMaster, wearing his uniform, sat next to him. “I watched and read a lot over the last two days. He is highly respected by everyone in the military, and we’re very honored to have him.”The choice continued Mr. Trump’s reliance on high-ranking military officers to advise him on national security. Mr. Flynn is a retired three-star general and Mr. Mattis a retired four-star general. John F. Kelly, the homeland security secretary, is a retired Marine general. Mr. Trump’s first choice to replace Mr. Flynn, Robert S. Harward, who turned down the job, and two other finalists were current or former senior officers as well. General McMaster will remain on active duty.General McMaster, 54, made a name for himself as a young officer with a searing critique of the Joint Chiefs of Staff for their performance during the Vietnam War and later criticized the way President George W. Bush’s administration went to war in Iraq.As a commander, he was credited with demonstrating how a different counterterrorism strategy could defeat insurgents in Iraq, providing the basis for the change in approach that Gen. David H. Petraeus adopted to shift momentum in a war the United States was on the verge of losing.Like Mr. Mattis, General McMaster is physically unimposing. But he is known as smart and soft-spoken with a sense of humor. For all of his war-making experience, however, he has little background in navigating Washington politics, which could be a challenge for him in his new role with a fractious national security team to corral.His challenge now will be to take over a rattled and demoralized National Security Council apparatus that bristled at Mr. Flynn’s leadership and remains uncertain about its place in the White House given the foreign policy interests of Stephen K. Bannon, the former Breitbart News chairman who is the president’s chief strategist.Most of the National Security Council staff is composed of career professionals, often on loan from military or civilian agencies, and they have complained privately about being shut out of their areas of expertise and kept in the dark about important decisions. Mr. Trump’s aides look on many of those holdovers from the last administration with suspicion, blaming them for leaks. The atmosphere has grown so toxic that some council staff members have said they feared they were being surveilled.Several security council aides said Monday that they learned about General McMaster’s selection the same way the public did and expressed concern that Mr. Flynn’s associates, nicknamed the Flynnstones, would still stick around. The White House has said it promised the original first choice complete autonomy in picking staff members, and it seems likely that General McMaster would insist on the same.Most of the National Security Council staff is composed of career professionals, often on loan from military or civilian agencies, and they have complained privately about being shut out of their areas of expertise and kept in the dark about important decisions. Mr. Trump’s aides look on many of those holdovers from the last administration with suspicion, blaming them for leaks. The atmosphere has grown so toxic that some council staff members have said they feared they were being surveilled.Several security council aides said Monday that they learned about General McMaster’s selection the same way the public did and expressed concern that Mr. Flynn’s associates, nicknamed the Flynnstones, would still stick around. The White House has said it promised the original first choice complete autonomy in picking staff members, and it seems likely that General McMaster would insist on the same.Source: The New York Times