Who will challenge and check the military now that Sen. John McCain is gone? The military shouldn't be an unchecked institution. John McCain was one of few politicians with the knowledge and backbone to stand up to the Pentagon.

John Spencer and Lionel Beehner | Opinion contributors

Sen. John McCain was more than just a maverick. He was a check against one of Washington’s most powerful government bureaucracies: the military.

There have been few political leaders willing to risk their political fate and challenge military dogma. McCain, a decorated veteran, was one of the few such leaders, a man who had the military knowledge and fortitude to hold our generals and admirals accountable. His absence will be felt the next time we hold hearings on the progress of our stalled wars.

Officers testifying on Capitol Hill feared his tough questioning, whether in a Senate confirmation hearing, a budget proposal or a strategy rollout. In 2010, Gen. David Petraeus even fainted during his appearance before the Senate Armed Services committee while being grilled by McCain on his Afghan policy.

Sure, at times he was a cheerleader of America’s post-9/11 wars. Yet, McCain challenged assumptions made by politicians beating war drums. For example, he opposed the use of so called “expanded interrogation techniques” as torture.

McCain fought wasteful military spending

He called for the military, so often resistant to change, to be more efficient — which is like asking the sun to be less hot. He fought against the Air Force's expensive F-22 program and the Navy's Littoral Combat Ship. McCain also sought to update the landmark 1986 Goldwater-Nichols Act, which restructured the services and made them a more unified operation. His goal was to streamline the procurement process to avoid wasteful spending and long delays. And he supported a faster rollout of MRAP vehicles to protect soldiers in Iraq.

McCain's unheralded role in Washington — as a persistent check on the military that is stubborn and sometimes arrogant in its ways — is an endangered species.

We lost Rep. Ike Skelton in 2013, a member of this small class of legislators willing to sacrifice political goodwill to challenge the military. For over 30 years, Skelton forced the military to reform its military professional education system.

More: John McCain, stormy and unchangeable, taught us to never give in to torture

McCain wanted to 'raise hell' and leave it all on the field. Mission accomplished, Senator.

What I learned about John McCain during 20 years covering him

At a time when the military is being given one of the biggest defense budgets in modern American history, when the war in Afghanistan is entering its 18th year, and when Trump has chosen to surround himself with three and four star generals, we need people like McCain and Skelton — veterans with deep military knowledge — on Capitol Hill more than ever.

There are only a few lawmakers left, such as Sen. Lindsey Graham, who have the knowledge and clout to challenge our military institutions.

Eisenhower famously warned of an unchecked military industrial complex. In today’s hyper-partisan world, we face a different kind of complex — a military with virtually little informed oversight, accorded so much respect by the public that to merely question its missions is to have one’s patriotism called into question.

Veterans must run for office

Rather than having retired flag officers on FOX or CNN spouting their political views, we need more veterans seeking political office. That is how we can ensure that the military will have a knowledgeable hall monitor to rein in the worst and wasteful of its bureaucratic tendencies.

Over 400 former service members are running or have run for national office in this year’s midterms, including a number of female veterans. Still, less than 20 percent of the representatives and senators in Congress have served. By contrast, 45 years ago, during the height of the Vietnam War era, the numbers of veterans in Congress exceeded 75 percent.

The military should not be an unchecked institution. Like any other agency in Washington, it requires oversight and monitoring. McCain was one of the few voices willing to call the military out.

What we need are more mavericks like him in Congress.

John Spencer is a retired major who served 25 years in the U.S. Army. Follow him on Twitter: @SpencerGuard. Lionel Beehner is an assistant professor and director of research at West Point's Modern War Institute.