With Congress away, President Barack Obama looks ready to grab some easy headlines this week by announcing his choices to sit on the last three empty shelves in his Cabinet.

If all goes according to expectation, he’ll end up with a group just slightly more demographically diverse than the team that was with him when he won re-election. But outside their formalized spheres of power, they’ll have no more influence over legislation or administration policy than the Cabinet members of Obama’s first term or, for that matter, of any such group during the past couple of decades.

And so any senators who may consider fretting about a Cabinet confirmation vote can confine the worry to the topics in the official job description.

If he gets to be Transportation secretary, as Obama proposed on Monday, Anthony Foxx would have no more sway over creating a guest worker program than he would have if he’d stayed mayor of Charlotte, N.C. Maybe less, given how important immigrant labor is to the North Carolina economy.

If the president asks and the Senate agrees to let Penny Pritzker move into the grandest of the corner offices at the Commerce Department, she will have less influence over the potential intervention in Syria than she would have had she remained a politically active and generous philanthropist. And she’ll have none of clout shaping school policy that she had in her last post, on the Chicago Board of Education.

The Cabinet is one of the government’s most misunderstood institutions. It’s mentioned nowhere in the Constitution and its membership has been evolving on the whims of presidents since George Washington.

It has evolved into an institutionalized component of the modern presidency  in a way that bears little resemblance to what the civics textbooks describe: a presidential board of advisers, or even a “senior table” or “executive committee” like you hear about in the corporate world, that convenes regularly to help the CEO settle on a path through the major dilemmas of the day.

Dwight D. Eisenhower was the last president, more than half a century ago, who followed that model at all closely. Bill Clinton and George W. Bush both talked about emulating Ike, but soon enough concluded that the system wouldn’t work. The department and agency bosses would inevitably resort to spending all their energies promoting their own positions and defending their own turf.

And so the architectural symbol of executive power during the past two decades has been the warren of small and often windowless offices of the West Wing — not the Cabinet Room with its French doors onto the Rose Garden.

Obama has never made any pretense about reviving the “strong Cabinet” model, and in fact his first term was peppered with complaints from Congress about too much decision-making clout residing with the non-confirmed policy “czars” and special assistants who tend to spend more time in the Oval Office than anyone with “secretary” in her or his title.

Which is not to say the people in the Cabinet are unimportant; it’s just that more often than not their sway stops at their own metaphorical doorstep. Inside their own fiefdoms their power can be phenomenal and, depending on their own political skills, they can develop a national following.

Ray LaHood’s crusade against distracted driving has made him as close to a household name as any other domestic department head in recent memory; the outgoing Transportation secretary may be remembered as the most successful former congressional chief of staff or House member to hold such a senior administration position, especially so when you consider he’s a member of a party different than the president’s.

Being a Republican, of course, was LaHood’s way of adding diversity to the initial group assembled by Obama. In 2008, the president followed the practice of his recent predecessors and filled his Cabinet with a collection of people who reflected the principle that the government’s top tier of managers should somewhat reflect the nation’s diversity.

It was Clinton who first elevated the notion that the Cabinet should “look like America,” and, in 1993, only six white men were in the core group of 14 — the executive department heads in the presidential line of succession. Eight years later, seven white men were on Bush’s 14-secretary roster, and the number slipped back to six again at the outset of the Obama presidency, even though by then the number of positions had grown with the creation of the Department of Homeland Security.

And now?  Assuming the confirmation of Foxx, the number of white guys in the Cabinet once again will be six — suggesting that Obama and his personnel team ended up with the same level of diversity they took so much grief for ignoring in the early weeks after the re-election.

It was almost certainly through painstaking hard work, not the serendipity that might come in a truly post-racial, gender-neutral political world.

But the demographic diorama in the Cabinet is shaping up to look much as it did eight years ago.