The question’s surprisingly hard but we should probably start thinking about it since, unlike Cruz’s pick, this one really might end up a heartbeat away.

Here’s the challenge in gaming this out. First, decide whether you think Trump will go for an insider, in order to reassure the electorate (and establishment Republicans) that he’s prepared to govern like a pro, or an outsider, in order to reassure his base that he’s serious about changing the way Washington operates. Once you’ve come to a conclusion about that, try to find someone who fits the bill and doesn’t otherwise have a future in the Republican Party. After all, if the odds of a Trump victory in November are as long as the conventional wisdom says, no up-and-coming GOP pol will accept an offer to be VP. No one’s climbing aboard a ship that everyone expects will sink, and no one’s signing up to defend Trump’s daily “I like soldiers who weren’t captured” deep thought — unless, that is, they have nothing to lose in doing so. That’s why Cruz, for instance, wouldn’t agree to become Trump’s number two (I think). Even if Trump likes him as a fellow “outsider,” Cruz almost certainly plans to run for president again in the future. Why risk crashing and burning with Trump this fall and then suffering recriminations from grassroots conservatives angry at everyone who enabled Trumpism? There’s nothing in it for Cruz, so he won’t bite. For the same reasons, neither would Marco Rubio or Scott Walker.

Same goes for Nikki Haley and Susana Martinez, two governors on everyone’s VP shortlist. They’re both potential presidential or vice presidential candidates in 2020; they’d be suckers to risk that with Trump, especially since Haley and Martinez each enjoy some buzz as GOP leaders who don’t come from the usual “older white guy” mold. The last thing either of them needs if they’re planning a national run down the line aimed at a new, more diverse Republican Party is being stuck spinning Trump’s thoughts on immigration and “Mexican rapists” for three months. Martinez surely knows how brutal Trump’s favorable rating is with Latinos right now and Haley would be an odd choice after having criticized Trump (albeit not by name) in her SOTU rebuttal and then endorsed Rubio in South Carolina. I don’t think it’ll be them.

Christie’s an obvious possibility given that he shares Trump’s tough-guy temperament, was an early adapter in endorsing Trump, and importantly doesn’t have any serious chance of higher office in the future. He’s already so closely identified with Trump in Republicans’ minds that he has nothing to lose by accepting the VP slot. He’s already all-in; might as well get something in return. The problem with Christie, I think, is the regional overlap with Trump. Why would Trump want a guy from his own backyard instead of from the heartland or the midwest to try to put Ohio, Wisconsin, and Minnesota in play? And beyond that, why would you waste Christie in the VP role when he seems tailor-made to be the sort of thuggish attack-dog Attorney General that Trump would instinctively crave? He’s much better suited personality-wise to ordering DEA raids of marijuana shops in states where weed is legal than standing at podiums next to Trump, holding his jacket and gazing at him adoringly. Although, in fairness, he’s really good at that too.

Ben Carson, then? A few months ago I would have said sure. He’s as much of an outsider as Trump could reasonably hope to find and he seems uninterested in running for office again. He’d be a living rebuttal to the inevitable charges from Democrats that Trump is a racist. He also wouldn’t blink at Trump’s less, shall we say, politically correct statements the way a more polished politician would. But you know already what the problem with Carson is: He is, quite simply, an historically bad surrogate. He’s constantly bumbling into statements that undermine Trump and reveal how tepid his own support is for him. For cripes sake, he told a radio host who’d called Trump a bad man and someone she could never vote for that he’d be right there with her if not for the horrible prospect of Hillary Clinton appointing Supreme Court justices. Trump’s not going to risk that sort of mega-gaffe from his choice of VP on the biggest stage in American politics this fall. Ironically, I think Carson’s too much of a loose cannon for the loose cannon.

I hear Newt Gingrich’s name thrown around sometimes, probably because of the sheer absurdity of the lengths he’s gone to in order to associate himself with Trump, but Newt’s had no role in the campaign apart from appearances on Fox. It’d feel strange to rescue a long-since-retired refugee from the Reagan revolution, who’s not nearly as much of an outsider as he now postures as being, for the VP slot when so many younger, more prominent Republicans are in the mix. One out-of-the-box suggestion I’ve always found intriguing is Jim Webb, a Republican turned Democrat who could form a fusion ticket with Trump, the Democrat turned, um, “Republican.” Webb is a Jacksonian to the core, which is perfect for Trump’s base, and he has enough government experience to give him a hybrid insider/outsider appeal that Trump might find attractive. A Trump/Webb ticket would run as a de facto independent ticket, a symbol that Trump was reaching out to Democrats in the general election and proof that he’s serious when he says there’ll be no more politics as usual under a Trump administration. The problem is, putting a Democrat on the ticket would also convince conservatives that Trump is a de facto independent, which is risky for turnout in the fall. Just for starters, Webb is pro-choice; he’d have to at least pretend to be pro-life a la his running mate. And then there’s the small matter of Webb being a war hero, an outspoken maverick, and an all-around alpha male. He’s the opposite of a yes-man, pure anathema to a narcissist like Trump. Making him VP would run a serious risk of Webb publicly disagreeing with the administration on various policy moves, which Trump couldn’t handle. It’d never work.

So, by process of elimination, it has to be Jeff Sessions, right? He’s not angling for higher office (he’s approaching 70). He has some insider credentials as a longtime member of the Senate but also loads of populist credibility as the congressional GOP’s staunchest critic of amnesty. He endorsed Trump despite Cruz’s tireless efforts to win him over, and he’s closer to Trump’s protectionist views than any other prominent Republican elected official. He represents a concession by Trump to the party’s southern base, and he seems congenial enough that he wouldn’t have the difficulty that Webb would defending Trump’s policies as a matter of course. I think he’s the pick. The only X factor in all this, to me, is whether any of the GOP’s younger stars — Cruz, Haley, Rubio, Walker, etc — might actually see a long-term opportunity in hitching themselves to Trump’s wagon for a short ride to electoral oblivion in November. The calculation would be this: If Trump’s voters are planning on sticking around within the GOP for the 2020 primaries, a candidate who can appeal to them and to grassroots conservatives would be able to draw on both of the party’s core constituencies instead of fighting for votes within just one. Cruz tried that strategy already, in fact, via his “bromance” with Trump last year, but that fell apart when Trump’s numbers wouldn’t fade and Cruz had no choice but to attack him. Cruz needs to rebuild some goodwill with Trump fans now and the shortest path to doing that is agreeing to accept the VP slot. Republican leaders and Trump fans alike would be grateful to him for doing his part to unify the party. And if, as expected, the ticket goes down in flames, Cruz can and would argue that he bore no responsibility for that. Everyone knew Trump’s favorables were horrific before he was nominated, when Cruz was still battling him at every turn, and those numbers bore fruit in November. I think there’s a small chance that some Republican, whether Cruz himself or someone else, will view the VP slot that way, as a potentially low-cost way to build a bridge to Trumpists for 2020 rather than as a political dead end. But if I had to bet, I’d bet Sessions.