I wrote about Mattis’s chances last month so read that if you’re interested in whether this could have worked or not. (Not.) The threshold problem was this: What was in it for Mattis? Why would an esteemed Marine commander, who’d avoided petty politics his whole life, decide to become a candidate in a race in which he had no chance of winning a single state? This was never going to be an Eisenhower situation where the Republican Party recruited him and handed him the institutional infrastructure needed to run a national campaign. He was going to need to build it himself, as an amateur, at the highest level, without any plausible path to victory. Either he would have crippled Trump’s chances, in which case his legacy would be “handed the presidency to Hillary Clinton,” or he would have been a nonfactor in the race, in which case his legacy would be “powerless to stop the Trump circus.” A man who’s served his country honorably for decades deserves a better legacy than that.

So, no go, although there is news here. Turns out Mattis was thinking harder about this than most people knew.

Two allies of Mr. Mattis sent emails to associates on Friday notifying them that the retired general had closed the door on a campaign. William Kristol, editor of the conservative Weekly Standard magazine, said Mr. Mattis had decided “after much consideration” not to proceed…

Joel Searby, a Republican strategist involved in laying the groundwork for a potential Mattis campaign, wrote in a separate email that Mr. Mattis had “decided definitively not to pursue a run for president.”…

In private, Mr. Mattis, 65, was receptive to political overtures: During a visit to Washington last Friday, he met with a small group of strategists supportive of his entry into the race and discussed the election, according to people familiar with the meeting, who spoke on condition of anonymity about the private session.

Kristol was asked about Mattis on “This Week” last weekend and noted that Mattis is a “social liberal,” which would have made him a not-entirely-perfect match for rock-ribbed conservatives who are disgusted with Trump and want another option. How conservative is Mattis, exactly? A distinguished military career, which he has in spades, can compensate for a lot of ideological heresies, but not all of them. If he’s pro-choice, pro-gay-marriage, and supports expanding gun control (I don’t know that he takes any of those positions, I’m just speculating), how many #NeverTrumpers would have backed him this fall?

Which brings us to an important point. If the “Stop Trump” crowd is serious about recruiting a third-party candidate (which I don’t think they are, but whatever), they need to decide up front if they’re going to make a play to win or if their goal consists entirely in siphoning off votes from Trump and denying him any chance at the White House. Whom you recruit will vary wildly depending upon which goal you’re pursuing. If you’re trying to win by somehow denying 270 EVs to both Clinton and Trump, which would send the election to the Republican House, logically you need someone who can steal at least one red state and one blue state. That means a centrist, and that’s why Mike Bloomberg’s third-party chances were, at least on paper, a bit better than most prospective independents. He would have won some votes from both parties. By contrast, someone like Tom Coburn, whose name has been floated as a potential anti-Trump independent candidate, would win conservative votes exclusively and therefore would achieve nothing except splitting Republicans with Trump, enabling a Clinton victory. Which is fine for some #NeverTrumpers; blocking Trump is the mission, whatever the cost, and a Coburn type would help with that. Actually electing a third-party candidate is a way more ambitious mission, and almost certainly impossible. And it comes with a risk for anti-Trumpers: If you make a play for the center, there’s a chance you’ll pull more votes from Hillary than you will from Trump, which would increase Trump’s chances of winning. Bloomberg stood a chance of doing that, in fact, to the point where Trump said publicly he hoped Bloomy would run. If your top priority is keeping Trump away from the presidency, backing a centrist is a gamble that backing a Coburn-type isn’t. Know your goal before you start the mission.

By the way, apropos of nothing, I continue to think David Petraeus would have been polling very, very well right now, especially on the right, if he hadn’t torpedoed his career with that scandal. He has what Mattis sorely lacks, widespread name recognition. “If he could get Iraq under control,” people would have said, “he can do it for America.” The guy blew an enormous opportunity, which I’m sure he never saw coming, when he strayed. I wonder how often he thinks about it.