It was only a few weeks ago that Vice President Biden ended months of misguided speculation by affirming that he wouldn’t run for president. But now there’s rumor of another possible last-minute bid, this time on the Republican side.

“[S]ome in the party establishment are so desperate to change the dynamic that they are talking anew about drafting [Mitt] Romney,” reported the Washington Post’s Philip Rucker and Robert Costa on Friday. “Friends have mapped out a strategy for a late entry to pick up delegates and vie for the nomination in a convention fight, according to the Republicans who were briefed on the talks, though Romney has shown no indication of reviving his interest.”

Mitt Romney’s making a comeback? Errrr, probably not. Historically, rumored eleventh-hour bids like these have almost never come to fruition. It’s not just Biden: Until quite late in the 2012 campaign cycle, there were reports that various candidates — Chris Christie, Paul Ryan, Jeb Bush, etc. — might enter the race to challenge Romney. None of them did.

But forget that for a second. (Also forget that when candidates like Fred Thompson and Wesley Clark have launched their bids late, they’ve tended to crash and burn — and that Romney’s bid would be even later than theirs.) Instead, let’s play along.

Unlike Biden, whose quasi-candidacy never had a coherent rationale except as a hedge against a major Hillary Clinton scandal, Romney would be entering a race without a dominant frontrunner. Donald Trump and Ben Carson remain atop the polls. Marco Rubio appears to be in the best position of any establishment candidate, but that’s like having the closest seat to the buffet table at an offensive lineman’s wedding; there’s still a lot of jostling to go before anyone gets their grub.

The only thing the GOP establishment seems to agree upon is that it doesn’t want Trump or Carson to be the nominee. So if the GOP wants to minimize the chance of one of them being nominated, does it make sense to support a Romney campaign?

The answer depends on your theory of why Trump and Carson are leading in the polls. If the GOP has chosen the wrong theory, then throwing its support behind Romney could backfire.

(I’m assuming, by the way, that candidates like Rubio and Jeb Bush wouldn’t instantly drop their bids just because Romney entered the race. Romney would begin with a foothold of establishment support, but would have to fight to win the rest of it.)

Theory No. 1: “It’s just a phase”

This theory holds that the polls showing Trump and Carson ahead don’t mean very much. After all, polls historically haven’t been very reliable at this stage of the campaign; just ask past frontrunners like Howard Dean, Rudy Giuliani and Herman Cain.

Furthermore, the theory (which heavily overlaps with “The Party Decides” hypothesis that we discuss frequently at FiveThirtyEight) implies that there’s no need for the GOP establishment to panic since it will probably win in the end. There are lots of campaigns that look chaotic until the first few states vote, but don’t wind up being all that close. Establishment-backed candidates such as John Kerry in 2004 and John McCain in 2008 rocketed into a strong position after the first few states voted and never really looked back. So did Romney in 2012, after a couple of bumps in the road.

If this theory is right, there are already several credible establishment candidates in the race, so there isn’t really need for another one. Thus, supporting Romney would be superfluous at best. And at worst, it would risk backtracking for an establishment that is increasingly coming to a consensus around Rubio and has several backup options (like Bush and Christie) should Rubio falter.

Theory No. 2: “This time is different”

This theory is just the opposite; it posits that those polls showing Trump and Carson ahead are the latest sign that Republicans are in disarray and that the Republican grassroots is rejecting the establishment’s ambitions.

If this is the case, the establishment might be screwed no matter what it does, but it certainly wouldn’t help to divide what remaining juice it has. Instead, the establishment would want to gird itself for a long and nasty fight. And it would want to go to battle not with a porcelain figurine of the establishment like Romney or Bush, but instead with someone who had some crossover potential: Rubio, for instance, who once was thought of as a tea party candidate, or even Ted Cruz, who for all his beefs with the GOP establishment might represent a more acceptable choice to them than Carson or Trump.

Theory No. 3: “Republicans just haven’t met the right guy/girl yet”

Under this theory, there isn’t anything systematic going on. Rather, the failures of the current establishment candidates reflect their failings as individuals. Bush is too moderate and a rusty, “low-energy” campaigner, the theory might hold. John Kasich, despite having good credentials, has adopted an ill-advised strategy that has him running too far to the left. Scott Walker was a gaffe machine whose retail skills didn’t translate beyond Wisconsin’s borders. Rubio? The jury’s still out, but he may be too young (read: too much like Barack Obama) and his support for immigration reform could come back to haunt him.

In this case, Romney would make some sense. He’s already shown he has the stuff to win a Republican nomination, after all. And he retains a reasonably good image with the party, with a 74 percent favorable rating among Republicans in a poll conducted late last year.

The problem with this theory is that it’s the least plausible of the four, statistically. Sure, some candidates with good credentials on paper — Ed Muskie or Phil Gramm, for example — prove to be duds on the campaign trail. Imagine that 50 percent of otherwise-well-qualified candidates are duds. How likely is it that Bush and Kasich and Rubio and Walker and Chris Christie and Bobby Jindal and Rick Perry are all duds simultaneously? (Not to mention all the other plausible establishment contenders in the GOP’s historically deep and well-qualified field.) Not very likely at all; it would be equivalent to flipping “tails” on a fair coin seven times in a row, the probability of which is 1-in-128.

Furthermore, it’s not as though Romney is a once-in-a-generation political talent along the lines of Bill Clinton or Ronald Reagan. Instead, his performance against Obama was no better than might be expected (and perhaps a bit worse) on the basis of economic conditions, and Republicans were constantly fretting about his political skills four years ago.

So to recap: So far we have two theories under which a Romney campaign would be somewhere between pointless at best and counterproductive at worst. And we have a third theory which relies on an implausible reading of the evidence. It’s not looking very good for the Mittster.

But there’s a fourth theory under which Romney could possibly help the GOP.

Theory No. 4: Chaos Theory

I’m going to get a little philosophical here. Both journalists and academics tend to prefer deterministic explanations of presidential campaigns. Sure, their outcomes might not be so easy to predict ahead of time. But, this position holds, that only reflects our imperfect knowledge of the initial conditions; once we observe the outcome, we know that the campaign was destined to turn out as it did.

But what if campaigns are not merely hard to predict but are actually a little random? Or perhaps even a lot random? Change one small thing just slightly — a debate moderator allows a follow-up response instead of nixing one; a candidate gets food poisoning on the eve of an important primary — and the outcome winds up being not just a little bit different but potentially way different.

I don’t think this idea holds up so well for general elections, where a good percentage of voting can be explained by partisanship, incumbency, economic conditions and other “fundamental” factors. But nomination races are different; they may literally be a bit chaotic. Timing and momentum can matter a lot: In 2012, for instance, Rick Santorum may have benefited from a lucky poll that triggered favorable media coverage and helped him to break his deadlock with other conservative candidates and win the Iowa caucus. That Iowa showing, in turn, helped to make Santorum the principal alternative to Romney, and he remained in the race until April. Absent that poll, Santorum might have been out of the race as fast as Michele Bachmann.

The more candidates who are running, the more potential for chaos. Walker’s abortive campaign, for instance, may have been a result of unlucky timing and an overcrowded Republican field rather than anything major he did wrong.

Wouldn’t a Romney bid — in a field that still has 15 active candidates — invite even more chaos? Maybe, but under this theory, the GOP is probably unlucky to have wound up in a world where Trump and Carson are doing so well. Doing something to shake the campaign up could be a good risk, therefore. Furthermore, Romney would potentially begin his campaign with a lot of momentum. He was polling at about 20 percent of the GOP field when he was considering a bid last winter. If he started out in the same place now, he’d be at or near the top of the field, which could encourage Republicans to join the bandwagon and consolidate behind him.

Sound a little risky? Absolutely. So we’ll counter chaos theory with Occam’s razor. If Jeb Bush and Marco Rubio and Scott Walker have all failed to bridge the gap between the establishment and the grassroots, bringing Willard Mitt Romney out of mothballs probably won’t help.