WASHINGTON — The Senate confirmed Mark T. Esper as secretary of defense on Tuesday, ending the longest period by far that the Pentagon has been without a permanent leader at its helm.
Mr. Esper, an Army infantryman who fought in the Persian Gulf war of 1991 before becoming a lobbyist for the military contractor Raytheon, replaces Jim Mattis, who resigned in December during a dispute over pulling American troops out of Syria.
In receiving the Senate nod, Mr. Esper has succeeded where Patrick M. Shanahan, President Trump’s original pick to replace Mr. Mattis, did not; Mr. Shanahan abruptly resigned last month, before his Senate confirmation hearing was even scheduled, after news reports revealed details of his 2011 divorce.
Mr. Esper now takes control of the country’s 1.2 million active-duty troops and one of the largest militaries in the world as the Trump administration is wrestling with the results of its so-called maximum pressure campaign of economic sanctions on Iran, which has prodded the two adversaries closer to military confrontation.
Mr. Esper will now add his voice to the senior Trump national security advisers seeking to influence the president on a range of issues, including how to end the war in Afghanistan, and how to negotiate with Turkey as the country, a longtime North Atlantic Treaty Organization ally, goes against American wishes in buying a missile system from Russia.
How influential Mr. Esper will be is one of the biggest questions facing the new defense secretary. Mr. Mattis was widely viewed as a voice of reason and global stability in a chaotic administration, but those very views helped to poison the relationship between Mr. Trump and Mr. Mattis, and led to Mr. Mattis’s resignation.
Mr. Shanahan, a former Boeing executive, by contrast, was seen as far more amenable to White House directives.
Unlike Mr. Shanahan, Mr. Esper joins Mr. Trump’s senior advisers with a solid background in military affairs and a broad understanding of the alliances that the United States has maintained throughout the Cold War era. But the exit of Mr. Mattis and the Pentagon’s seven months without a permanent secretary have diminished the department’s voice in internal White House meetings.
Meanwhile, the national security adviser, John R. Bolton, and Secretary of State Mike Pompeo — who was a former West Point classmate of Mr. Esper — have largely run national security policy in the months since Mr. Mattis departed. Mr. Esper’s challenge, national security experts said, will be to work to get the Pentagon’s views represented among those strong personalities.