A well-known military adage wryly notes that no plan ever survives first contact with the enemy. The same could be said of proposed defense budgets. Though in this case, it’s not an opposing army that usually threatens to undo an administration’s best-laid plans but rather the United States Congress. As frustrating as it may be for Pentagon officials, that’s the way the authors of the Constitution intended it to work. But in an election year, with intense partisan debate over spending and revenue, the possibility of a total stalemate on the defense budget looms very large. With American forces still fighting in Afghanistan, and with Iran and North Korea remaining potential flash-points, the consequences could be grave.

Over the past several weeks, the Obama administration has rolled out both a new defense strategy and a proposed defense budget for the coming fiscal year. The two are inextricably linked. After all, a strategy is only so much ink on paper without the resources required to implement it. And resources right now are tight. In crafting its budget proposal, the Pentagon had to grapple with a nearly half-a-trillion dollar cut in projected spending over the next decade. Some very difficult trade-offs had to be made. According to senior Defense officials, the resulting proposal represents a carefully constructed, integral package. They have thus urged legislators not to “cherry pick” those parts of the budget they’ll support and those they’ll reject.

That’s wishful thinking. Congress takes very seriously its powers and prerogatives to provide for the common defense and has historically put its own stamp on defense budgets. In fact, legislators began to voice concerns about elements of the current proposal even before it officially arrived on Capitol Hill last month.

A case in point is the air force’s plan to reduce the size of the Air National Guard. As part of its effort to trim its ranks by nearly ten thousand airmen over the next five years, the service called for more than half of the personnel cuts to come from the guard. It also proposed moving some Guard flying units between states. Air force officials have argued that the right mix between active, reserve and guard forces has to be struck in order to properly balance their respective workloads within a shrinking air force.

From the very outset, the air force’s plans for the guard were not likely to win the hearts and minds of legislators concerned about jobs in their districts—especially in an election year. Not surprisingly, members of Congress have sharply questioned air force officials on this issue during recent hearings. Additionally, a bipartisan council of state governors has developed an alternative to the air force’s plan. In response, air force leaders say that they will “reconsider” some of the more controversial provisions of their original proposal.

This give-and-take over defense budgets has been a feature of American history since the very beginning of the Republic. It is, in part, the inevitable legacy of the checks and balances written into the Constitution to ensure civilian control of the military. It also reflects the dictum that all politics are local. In the end, a compromise defense budget usually gets passed, and a military force gets fielded.

The concern now is that in the current, highly polarized political environment, differences over the defense budget will not result in an acceptable compromise but in a deadlock that fails to produce a defense budget until after the November elections. In fact, over the past decade, Congress has failed on several occasions to pass a defense-appropriations act on time, leaving the military to operate on a so-called continuing resolution, with the possibility that even this stop-gap measure would not be passed in time to avert a shut down.

When this happens, the consequences for the military can be significant. Major modernization programs get pushed to the side; costs soar as industry stretches out the development and production cycles for new weapon systems. Worse yet, the ensuing uncertainty adversely impacts troop morale. The sergeant major of the army recently testified on Capitol Hill that “whether or not there will be an appropriations and authorization bill signed is on people's minds. The last thing we want to have is for some soldier, sailor, airman or Marine deployed in harm's way, being concerned about whether or not they are going to be paid.”

The administration and Congress should vigorously debate the proposed defense budget. That said, both sides should put a big red circle around September 30 on their respective calendars and commit to passing next year’s defense budget on time. If this essential task gets pushed past the election into a lame-duck session, it might not get done until well after the new Congress convenes in January. Meanwhile, the world remains an uncertain and unpredictable place.

Frank Klotz is a senior fellow at the Council on Foreign Relation in Washington, DC, and the former commander of Air Force Global Strike Command.