Mitt Romney fired the first real shot in what will be a weeks-long, multimillion-dollar battle by the Republican establishment to thwart Donald Trump from obtaining real power. As far as political speeches go, Romney's was quite good. Yet as many have observed, Romney was precisely the wrong messenger. Among Trump supporters, Romney's enmity toward Trump is viewed as a confirmation of their choice, not grounds for reconsideration.

But the question begs: If Romney is the wrong anti-Trump messenger, who is the right one?

The answer is David Petraeus, William McRaven, and the other members of America's decorated warrior class.

That Trump supporters do not place any stock in messages delivered by the GOP's failed 2012 nominee should be no surprise. Trump's rise is plainly fueled by a rebellion of his disillusioned supporters against the career politicians who have over-promised and under-delivered for years. Trump voters are firmly rejecting the conventions and rules of the political class. They're not going to listen when Mitt Romney, of all people, tells them to get back in line.

But it would be a mistake to believe that Trump's flaws do not matter to his supporters, or that they cannot see his flaws. They do, but they are willing to overlook those flaws because they perceive Trump as a strong, decisive winner.

The key to defeating Trump is to pop the "winning" bubble.

On domestic issues, Trump supporters are unlikely to be separated from their man. The only people who can claim to be better businessmen than Trump tend to behave much like politicians (or, in Romney's case, actually are politicians) thereby rendering them useless. Yet on national security matters, where Trump has repeatedly demonstrated himself to be utterly out of his depth, Trump can claim no real expertise. The problem to date is that the people pointing this out have been politicians whose grasp of nuance does not inspire respect or awe among Trump supporters.

Outside of this letter from national security leaders, Trump has yet to be truly challenged by a member of the warrior class outside of the political fray. But this is where Trump is truly vulnerable.

Trump routinely brags that he will win wars and defeat enemies. Yet if a giant of the warrior class — General David Petraeus and Admiral William McRaven come immediately to mind, as does General Stanley McChrystal — were to come out and make the case that Trump is dangerously out of his depth and would put American lives at risk with his poor judgment, Trump would find himself, for the first time, fighting an adversary that his admirers respect more than him. Whatever else they are, Trump's supporters remain fiercely patriotic, and they will never, ever vote for anyone they believe would harm America's power or needlessly put our troops in harm's way. Moreover, Trump supporters, many of whom are veterans themselves, are aware that he did not serve and has no claim to having ever fought a war, much less any knowledge of what it takes to win one.

David Petraeus is uniquely suited to the task of unmasking Trump as a military naif. While his extramarital affair was a grave error in judgment, Petraeus remains the greatest, most widely recognized military leader of his generation. He is also, with the possible exception of Colin Powell, far and away the most famous. If Petraeus and other members of the warrior class take to the morning shows and then fly to Florida to make the case to voters in person, Trump's supporters will listen carefully to what America's top warriors have to say. For unlike Trump, who claims to be a leader of men, General Petraeus and the other members of the warrior class have actually fought and defeated the enemies Trump claims will bow down to him.

To be clear, this military-led rhetorical attack on Trump cannot be an off-hand remark. The campaign will have to be sustained, concerted, and public. But if America's greatest retired warriors unite, they may do what no establishment figure ever could: Reach Trump's supporters and make them reconsider whether they are prepared to put the lives of our young men and women in the armed services in the hands of a man our greatest living military leaders deem dangerously unfit for the job of president of the United States.