ASHTON B. Carter, President Obama’s nominee to be his fourth defense secretary, is supremely qualified to manage the Pentagon. Even in a polarized Congress, he is likely to be swiftly confirmed. Having served seven years in senior defense positions, he is one of the nation’s foremost experts on the department’s most pressing challenges, including procurement, cyberwarfare, nuclear weapons and missile defense. Mr. Obama was no doubt correct to say Friday of Mr. Carter, a 60-year-old Rhodes scholar renowned for his intellect, that “on day one he’s going to hit the ground running.”

Mr. Carter will need that momentum. He takes over from a weak leader, Chuck Hagel, who never won the respect of the Pentagon and lost what he had at the White House. Defense faces potentially crippling budget problems, including a renewal next year of the drastic “sequester” cuts mandated by the 2011 budget law. In both the wars against the Islamic State and in Afghanistan, senior commanders have chafed at constraints imposed by Mr. Obama. The president’s first two defense secretaries, Robert Gates and Leon Panetta, accused the White House of micromanagement and excessive insularity, while Mr. Hagel was reported to have objected to Mr. Obama’s policies on Syria and Ukraine.

Because of his expertise and credibility with both parties, Mr. Carter may have a better chance of pushing through badly needed budget reforms. The Pentagon is struggling to pay for weapons systems like the F-35 plane in part because of huge cost overruns, but also because the proportion of the budget spent on non-warfare costs is rapidly growing. While the Army is being reduced to its smallest size since before World War II, and the Navy is on its way to having the fewest ships in a century, spending on retirees’ health care more than doubled from 2001 to 2012.

Congress has blocked even the modest cuts in health benefits and base costs sought by Mr. Obama. But Mr. Carter may find allies in the new chairs of the Senate and House armed services committees, Sen. John McCain (R-Ariz.) and Rep. Mac Thornberry (R-Tex.), who have campaigned for cutting Pentagon waste but oppose the indiscriminate slashing of the budget.

Whether Mr. Carter will have better luck than his predecessors in influencing national security policy is another question. While it’s hardly novel for the White House to make the big decisions about wars, Mr. Obama’s previous secretaries have been caught between the president’s coterie and senior commanders who believe, as Mr. Gates put it recently, that they have been given missions and then denied “the authorities they require to achieve the objective.” That is true in Iraq, where Mr. Obama has peremptorily ruled out the use of U.S. ground forces; in Syria, where he has resisted action to defend U.S.-backed rebels from the regime of Bashar al-Assad; and in Afghanistan, where he has repeatedly set arbitrary deadlines for the withdrawal of U.S. forces.

Mr. Carter told Mr. Obama on Friday that “if confirmed in this job, I pledge to you my most candid strategic advice.” We expect he will deliver on that; we hope the president will be listening.