Last week I did an extended meditation on Sean Trende’s observation that Mitt Romney just isn’t telling voters enough about his own personal background or his agenda to get him across the threshold of credibility as a presidential challenger, even if they are ready to “fire” Barack Obama. Let me repeat Sean’s key argument:

[T]hese are parts of his biography that simply must be filled in if Romney wants to win, along with his activities turning around the Salt Lake City Olympics. (Does anyone outside of the political world even know about that?) If Romney can do this, he’ll have an excellent shot at winning this race. It might not even be close. But if he can’t, he will probably become the first presidential challenger in modern history to pass Step 1 of the referendum model, but fail Step 2.

Sean wrote that before Romney’s blundering appearance in London cast serious doubts about the utility of his “Olympics Story,” previously the one bright shining exception to a long public and private career that he has chosen to obscure. Moreover, there is fresh evidence that voters just don’t like what little they know about the GOP nominee: a Pew survey showing Mitt’s favorability ratings (37/52) deep underwater. Pew’s analysis points out that the only two recent presidential nominees with net negative favorability ratings prior to Election Day (Bush 41 in 1992, Dole in 1996) lost. Moreover, while undecided voters in Pew’s survey don’t much like either candidate, Mitt’s numbers (18/57) are significantly worse than Obama’s (31/48). And it’s no longer possible to blame Romney’s bad personal favorability ratings on the misgivings of conservative Republicans who don’t like or trust him but will march to the polls to send him to the White House anyone: his favorability ratio among those intending for vote for him is now 79/12.

In the weeks just ahead, we’re going to hear a lot about Romney’s opportunity for a home-stretch “reboot” of his campaign. He’ll get to roll out his Veep. He’ll have the usual high-production-value convention that enables him to “reintroduce” himself to voters. He’ll deliver an acceptance speech that will draw more eyes and ears than anything he’s said and done up until now. And then there will be debates and all the brouhaha associated with the most intense stage of the campaign, in September and October.

That’s all entirely true. But the fact remains: what can Romney do to boost his favorability ratings if he’s unwilling to talk about his business background, release his taxes, discuss his record in Massachusetts, or go into details about his tax proposals or the Ryan Budget? According to virtually every source, he’s not going to take any risks in choosing a running-mate. What, exactly, will barnstorming around the midwest with Tim Pawlenty or Rob Portman do for him?

The race is obviously close enough that even a small turnaround in personal perceptions of Romney could be crucial, and the threshold he needs to cross could draw closer if the economy gets worse or Obama makes some mistake of his own. But at some point the man is probably going to have to change what he’s doing, not simply do more of what hasn’t been working up until now. And even if he does stand pat and hope for the “referendum effect” to take hold, big elements of the conservative chattering classes will almost certainly greet late-cycle reports of Romney weakness with shrill demands for Breitbartian viciousness against the incumbent (never a formula for boosting one’s favorability ratings) or loud-and-proud advocacy of exactly those features of the GOP agenda that swing voters are certain to reject.

I’m not one to assume that Romney and his brain trust are stupid or feckless, and if they can come up with an effective stretch-drive message that damages Obama while making Romney more palatable, they will have vast resources for driving it home and ensuring that the pre-mobilized conservative voter base shows up on Election Day. But there’s no way around the realization that Team Romney has painted itself into a very small corner with the decisions it has made (and that the candidate himself has made for many years), and will probably need to make some sort of significant leap to get itself out and across the finish line.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.