In South Carolina Saturday night, Mitt Romney warned Republicans that they can’t beat President Obama with another life-long politician who resorts to leftist attacks on investors. He also could have mentioned that the Republicans can’t attack Obama on his national security failings with a candidate who is both irresolute and lacking seriousness.

Both Romney and Rick Santorum are solid not only on the rhetoric but also on the policies needed to defeat the war against jihadist terror. Both condemn Obama’s premature withdrawals from Iraq and Afghanistan. Both condemn his defense cuts. Both are critical of his penchant to coddle dictators. Both have been critical of U.S. obsequiousness to China.

But Gingrich is another matter. When given a chance to play irresponsibly to the crowd in the debates, Gingrich declared (like Texas Gov. Rick Perry) that he’d zero out foreign aid and cut off Pakistan. During the Iraq surge he was erratic in the extreme, often playing to the left and decrying the Bush administration’s efforts to turn the war around.

Gingrich likes to call himself a “cheap hawk.” But serious lawmakers and analysts know that no matter how much waste, fraud and abuse we wring out of the defense budget, our aging military requires significant upgrades. Both Romney and Santorum have defended defense spending. Gingrich? Not really.

Then there is the matter of Gingrich’s belligerent tone. He revels in his cleverness, declaring Palestinian nationalism to be made up. (As is Jordanian nationalism, he neglects to mention.) This tickles his money man Sheldon Adelson but is obnoxiously destructive and unbecoming of someone actually seeking to lead a nation and influence affairs in the Middle East.

Gingrich’s desire to be a provocateur rather than a practical politician is most dangerous in the national security realm. It is there that his hyperbole and his desire to embrace ideas for political effect would lead to as much, if not more, chaos in our foreign affairs than we’ve seen under Obama. If Republicans want a resolute, steady commander in chief Gingrich is not their man.