Reihan Salam appears  to be a bit fuzzy on the concept of “last resort”:
Conservatives need to think seriously about how we might, in the words of Brookings defense analyst Kenneth Pollack, ”put pressure on Iran in various ways, to keep it on the defensive and to encourage the end of the regime.” A military strike might ultimately prove to be our best or our only option, but as the debate over Iran continues to unfold this year and next, it is vitally important that conservative candidates make it clear that war is their last resort [bold mine-DL].
Put another way, Salam wants conservative candidates to misrepresent their support for an illegal, unprovoked attack on Iran and claim it to be something that it clearly is not. If the U.S. attacked Iran, it wouldn’t be using force as a last resort. It would be launching an international war in violation of the U.N. Charter. Whoever supports attacking Iran has already rejected the idea that force should always be used as a last resort. If a candidate believed force should be used only as a last resort, he isn’t going to support attacking Iran, and he would presumably oppose any wars that aren’t in self-defense. What Salam is really saying here is that conservative candidates need to avoid appearing too aggressive in their support for military action because this will go over badly with most voters. These candidates may say that they believe force should used as a last resort, but their willingness to consider illegally attacking another country shows that they don’t mean it. It’s not possible to start a war as a last resort, but it is “vitally important” for these candidates’ election prospects to pretend that it is.
Salam cites a report  that includes a quote from North Carolina Sen. Richard Burr, who says, “I don’t think anybody in America believes that we’re on the verge of shipping a couple of hundred thousand troops somewhere to fight a war.” No, there probably isn’t anyone who believes that this is going to happen in the near future, but then an attack on Iran wouldn’t require anything like that to trigger a new and costly war all the same. Maybe Burr doesn’t want to be pinned down as a supporter of an illegal war, so he defines war as something involving hundreds of thousands of soldiers fighting in an Iraq-like conflict and says he isn’t for that. Is Burr also opposed to bombing Iran? The report never says either way, and Burr is permitted to create the impression that he is against attacking Iran when everything in his record  suggests that he would have no problem with it.