It’s not an easy task for a presidential candidate to decide when and how to criticize the incumbent on national security matters. No candidate wants to cede ground to the president, especially one with as troubling a record as this one. But neither should a challenger be excessive in ripping the commander in chief or refuse to acknowledge success.

Now some just want the president’s rival to shut up. President Obama rapped critics of his Iran policy for purportedly engaging in “loose war talk.” Last week, to the shock of some foreign policy hawks, Bill Kristol harshly scolded Mitt Romney for criticizing Obama’s handling of the Chen Guangcheng situation, which Romney had done in terms similar to most every conservative foreign policy guru who has spoken or written on the issue. (Dan Senor, the most prominent foreign policy surrogate, was also dispatched to critique the president’s performance.) Interestingly, on Friday, Chen’s lawyer remarked on the efficacy of public criticism of the president, “I knew Obama would sooner or later have to say something. How was he going to fight a campaign and respond to attacks by Romney? By sitting in silence?”

So what is a candidate like Romney to do?

First, silence on national security is not an option for someone vying to be commander in chief. Romney must show his own grasp of the issues and provide a clear contrast with the president on issues with which he disagrees. That’s why the Democratic National Committee chairwoman’s plea not to make Israel a campaign issue is preposterous — campaigns are precisely the right time to debate weighty matters and hold elected officials accountable for their record .

Second, the rule for when Romney should speak up on a given incident can’t be to wait until all facts are certain and the outcome is clear. Even presidents with access to the best available intelligence don’t have that luxury. Rather it is wise, precisely as Romney did in speaking on the Chen issue on the campaign trail and again on TV on Friday, to preface comments with the caveat that the criticisms as based on news reports which “if true” lead to some conclusions. Romney doesn’t have to be the first critic to pipe up when Obama stumbles, but neither should he be the last, thereby conveying the image of passivity and tentativeness.

Third, Romney should talk about foreign policy at times other than crises and screw-ups. Since Romney’s major foreign policy speech at The Citadel and release of a comprehensive white paper last year, his remarks on foreign policy have become sporadic and vague. He will impress voters and avoid charges of opportunism by talking more consistently and specifically about the president’s failings. Why not a major speech on human rights? Or Obama’s neglect of allies in our hemisphere?

Fourth, he should acknowledge success. Romney was smart to praise Obama for ordering the bin Laden raid, even as Obama was ungraciously and obnoxiously denying that Romney would have given the same order. Romney won’t be giving up that much by praising the administration’s foreign policy successes (there aren’t more than a few), will enhance his stature and emphasize what a petty, small-minded figure Obama has become.

Fifth, Romney should measure the president’s actions against his own goals and rhetoric. Obama said that he would improve our image in the Middle East; it’s now worse. Obama said that he would achieve a Middle East piece deal in a year or two; he made hash out of it. Obama was going to “reset” relations with Russia to gain greater cooperation; Vladi­mir Putin’s domestic repression and foreign behavior have gotten worse.

And finally, it’s critical for Romney to speak about Obama’s savaging the defense budget. This is the most destructive and potentially significant national security step Obama has undertaken. His own defense secretary declared that the sequestration cuts would be “devastating” to our national security. It is inexcusable that the president would oppose alternative cuts, increase the burden on our troops and their families and undermine our national security. It is baffling that Romney speaks so infrequently about it.

Romney has been hampered by the absence of a foreign policy spokesman. But more to the point, in the Boston conclave there is no foreign policy expert who consistently provides input and can integrate foreign policy into Romney’s message. That leaves foreign policy as an afterthought for the campaign. Romney would be smart to remedy these problems quickly. He is auditioning for commander in chief and he needs to act like he’s interested in the topic and confident about discussing Obama’s shortcomings.