One theory for why Chuck Hagel stepped down as secretary of Defense is that President Barack Obama wanted someone who would be a better salesperson for increasing Pentagon spending. If that’s the case, the president has crafted the wrong job description for the individual who will be called upon to manage the government’s most expensive, least-accountable agency.

Whoever takes up the post, the next secretary of Defense will face the same budgetary challenges that Chuck Hagel did — an overly ambitious agenda that doesn’t match the funds that are likely to be available to the department over the next five to 10 years.

Unfortunately the administration seems to be taking a step away from budget discipline even as it brings in new blood at the Pentagon. Press reports have indicated that the fiscal 2016 budget that will be released next February will seek a Pentagon top line that is up to $60 billion higher than the caps set by current law. This is an unrealistic approach that is likely to lead to sloppy budgeting and make it more difficult to set priorities.

Republican control of both houses of Congress will not make it any easier to increase Pentagon spending beyond the levels set by the Budget Control Act. The Republican majority will not want to sign off on a tax increase as one of its first official acts, and Democrats in Congress and the executive branch will continue to defend entitlement programs from significant cuts. That means there will be no grand bargain on the budget, and no lifting of the caps on Pentagon spending.

It’s conceivable that a partial lifting of the caps could be negotiated, along the lines of the Murray-Ryan budget deal of December 2013. But a mini deal will do little to bridge the huge gulf between likely funds and overly ambitious plans that prevails at the Pentagon.

There is no major area within the current Pentagon budget that is aligned with budgetary reality.

Military health care costs are skyrocketing, and so far Congress has refused to institute the modest reforms put forward by the Pentagon. Before leaving office, Secretary of Defense Robert Gates asserted that “health care costs are eating the Defense Department alive.” Nothing has changed since he made that statement three years ago.

The Pentagon bureaucracy remains overstaffed, with almost as many civilian employees as there are active duty troops. And that doesn’t even include the hundreds of thousands of private contractors that work in parallel with government employees. A 2013 report by the Stimson Center indicated that cutting these two categories while consolidating other parts of the Pentagon bureaucracy could save on the order of $15 billion per year.

Then come the services.

The Air Force wants the F-35 combat aircraft, a new bomber, a new refueling tanker, and a new generation of unmanned aerial systems. The F-35 alone — which is slated to be the most expensive weapons program ever undertaken by the Pentagon — will be hard enough to fund, without squeezing in three other major programs.

The Navy wants to build 12 new ballistic missile submarines at a total estimated cost of about $100 billion even as it builds new surface ships and tries to maintain its current level of aircraft carrier task forces. The money just isn’t there in the Navy’s shipbuilding budget, as the department has acknowledged by asking for a separate “sea-based deterrent fund” to pay for the subs. But this is just a budget gimmick that will do nothing to make the Pentagon’s total procurement plans more affordable.

Meanwhile, the Army would like to keep at least 490,000 troops, even though it is only funded for 420,000 under the administration’s current five year spending plan. Where will the additional funds come from?

In short, whoever is selected for the job, they will need to make some tough choices if they are to squeeze the Pentagon’s plans under the funding ceilings the department will almost surely face in the years to come. Hopefully, rather than getting into a rhetorical competition about who can sound tougher, some members of the Senate will ask tough questions about matching plans with resources during the confirmation hearings of the next secretary of Defense. Otherwise the new secretary is liable to continue pushing the department towards a budgetary train wreck that will undermine fiscal responsibility and prevent sound national security planning.

William D. Hartung is the director of the Arms and Security Project at the Center for International Policy.