JACK LEW, President Obama’s choice for Treasury secretary, is eminently qualified for the job. Currently White House chief of staff, Mr. Lew is able, honest, intelligent, deeply experienced in both politics and policy and a legitimate expert on the federal budget, the stabilization of which is bound to be a central preoccupation of Mr. Obama’s second term.

Do Republicans on Capitol Hill think Mr. Lew was overly confrontational during recent budget negotiations? Perhaps, but he was both responding in kind to GOP hardball and doing the bidding of his boss, Mr. Obama — who is entitled to a Cabinet of his choice, other things being equal. Barring some negative surprise during the confirmation process, the Senate should confirm Mr. Lew promptly.

But the second-term Cabinet taking shape gives rise to concerns nonetheless. Much has been made of the fact that Mr. Lew, CIA Director-designate John Brennan, Secretary of State-designate John F. Kerry and Defense Secretary-designate Chuck Hagel are all white men. Since Eric F. Holder, who is African American, is remaining as attorney general, there will be no women in these power positions.

Other types of diversity are also being shortchanged. Unlike many Treasury secretaries, Mr. Lew has scant high-level private-sector experience and no current attachment to the financial industry; nor does he have a long track record in financial regulation or crisis management. Mr. Obama, who pledged during the campaign to improve his administration’s relationship with the private sector and make it easier for companies to deal with Washington — he even talked about consolidating agencies under a single “Secretary of Business” — will have to develop other channels to do so.

So far Mr. Obama seems to be assembling a team of Washington insiders who are personally close to him — and thoroughly in sync with his left-of-center views and those of the Democratic Party’s base. (Yes, that applies also to Mr. Hagel, who, despite being a nominal Republican, shares the Democratic left’s skepticism toward the Pentagon budget.) That may seem the obvious thing for a president to do. But we’re struck by the contrast with Mr. Obama’s first-term Cabinet, which included his former rival for the Democratic nomination (Hillary Rodham Clinton), a seasoned moderate Republican of independent stature (Robert M. Gates) and an apolitical financial technocrat (Timothy F. Geithner). The president was much praised then, and rightly, for assembling a team that could challenge and question him as he formulated policy.

Mr. Obama seems to have decided that it’s time to close ranks and present a united front to the Republican opposition. This, too, may be understandable, in response to a GOP that in his first term showed little inclination for compromise. In girding openly for battle, however, the president may be closing off a range of perspectives and experiences, including some from outside his personal and political comfort zones — not to mention from outside the Beltway. That’s always a risk for second-term presidents anyway. To be sure, Mr. Obama has ample means to seek advice from outside his Cabinet and White House staff, and from the private sector. It will take some extra effort, but he would be wise to make it.