Now that Mitt Romney is the de facto Republican nominee, the political press corps can indulge in a compulsion as addictive as OxyContin and as frivolous as Angry Birds. The rules of the Pundits Guild stipulate that as soon as the news broke Tuesday afternoon that Rick Santorum was suspending his campaign, the vice-presidential frenzy had to begin without even a moment’s pause for rest or (yikes) reflection.

In truth, the press pack jumped the gun in the Heartbeat-Away Derby by anointing Romney as soon as he won the Wisconsin primary. Already we have been treated to a full-scale boomlet for Ohio Senator Rob Portman. The insider outlook was succinctly expressed last week by a Politico headline over a Maggie Haberman story: “Rob Portman tops veepstakes.” And the National Journal’s Major Garrett on Thursday offered one of those glib parallels that always pop up when speculating about the bottom of the ticket: “Portman is to Romney what Al Gore was to Bill Clinton.”

But not so fast, Vice President Portman. If the journalistic enthusiasm for Portman, a former George W. Bush budget director, is based on armchair psychological analysis about what Romney might theoretically want in a running mate, other reporters have been equally energetic in scrutinizing body language. Morgan Little, in the Los Angeles Times, recently observed, “If Romney’s campaigning in Wisconsin is any indication, Rep. Paul Ryan (R-Wis.) may be the new favorite.” Steve Holland in a Reuters dispatch Friday similarly noted, “The name most associated with Romney in the last week is Ryan who looked to have a personal chemistry with the former Massachusetts governor when they campaigned in Wisconsin.” There is always an inherent danger in allowing reporters this early in the vice presidential search to play with chemistry sets.

Meanwhile, Marco Rubio’s fortunes have bobbed like a flamingo’s head as it searches for food. The opening sentence of the Miami Herald story about the fledgling Florida senator’s late March endorsement of Romney included the obligatory “fueled speculation he is seeking a spot on the ticket.” But then skeptics began to take seriously Rubio’s boilerplate disavowals of interest. Time’s Michael Crowley was typical in concluding Friday, “I suspect Rubio may understand that his political stock may be overvalued.”

Whew. It’s going to be an exhausting four months until Romney takes us out of our collective misery by actually picking his own version of Mini-Me. Probing analysis and deft biographical portraits of vice presidential possibilities are valuable at any stage since nothing in a campaign for the White House is more important in future governing terms than the selection of a running mate. The problem comes when the press corps gets too far ahead of reality with the frenzied speculation about the results of an election with only one voter (Romney) who is keeping his thoughts to himself. Recent history suggests that treating the veepstakes like another political horse race invariably produces lame conclusions.

At this point in 2008, only a few conservative publications (most notably the Weekly Standard) were taking Sarah Palin seriously as John McCain’s running mate. (On the Democratic side, attention was still fixated on Hillary Clinton’s last stand against Barack Obama). While the pre-scandal-scarred John Edwards was on everyone’s 2004 VP short list, it did not prevent the New York Post from knocking wood with a banner, “IT’S GEPHARDT,” on the morning that John Kerry was scheduled to unveil his choice.

The campaign press pack would have done better with a dart board in 2000 than it did by ballyhooing the vice-presidential rumors passed along by political insiders. That April, Joe Lieberman was buried in long lists of possible Al Gore running mates and Dick Cheney had just been named as the impartial head of George W. Bush’s search committee. New York Daily News Washington bureau chief Thomas M. DeFrank captured the prevailing mood when he wrote on April 20, 2000, “Bush and Gore have said they haven’t yet compiled short lists of running mates, but Gov. Tom Ridge (R-Penn.) and Sen. Bob Graham (D-Fla.) frequently are mentioned by political insiders as leading contenders for their respective tickets.”

A major reason why premature veep speculation is prematurely wrong is because the presidential nominees have not made up their own minds or are about to change them. Vice presidential searches can shift direction in an instant even without the electric shock of a Tom Eagleton-like secret coming out during the final round of vetting. In 2008, according to Game Change by John Heileman and Mark Halperin, “For much of August, McCainworld pursued the [Joe] Lieberman option with a singular focus.” That initial preference, shared both by the candidate and his top advisers, was only abandoned when the McCain team belatedly realized the extent of potential right-wing rage over a potential running mate with liberal positions on most social issues.

In 1988, it was not until the Friday before the Republican Convention that George H.W. Bush got around to canvassing his top advisers for their veep picks. (Chief strategist Lee Atwater, of course, had already commissioned a raft of polling). While Dan Quayle had few enthusiastic supporters among the Bush inner circle, he also had the fewest detractors. Quayle’s only fervent opponent was campaign chairman James Baker. As a result, it is universally assumed that it was Baker who leaked Quayle’s name to the New York Times in the hopes of arousing opposition from Republicans who saw the Indiana senator as a real-life Alexander Throttlebottom. But Baker made a strategic error, as former Washington Post reporter Paul Taylor tells it in his 1990 book, See How They Run. Quayle was such a non-entity in the Senate that, according to Taylor, “even after the Times piece came out, virtually no one considered Quayle as a serious possibility.”

How I remember that egg-on-the-face feeling at the 1988 GOP Convention. As a senior writer for Time, I was learning the shocking life lesson that late nights in the bar and early morning interviews do not mix, especially in New Orleans. So the Monday morning of the convention, with Bush’s choice still under wraps, I rolled over when the hotel wakeup call summoned me to a Time breakfast with a long-shot vice-presidential possibility—a callow, golf-obsessed senator named Quayle. I still cringe with embarrassment that later that week I had to borrow a colleague’s tape of that breakfast in order to write the Time cover story about Bush’s quicksand problem with Quayle.

I am not a press-criticism purist who naively believes that a few high-minded lectures can stamp out bottom-feeding rumor-mongering about the bottom of the ticket. My dreams of reform are far more modest: Permanently deleting from news stories and TV commentary John Nance Garner’s (bowdlerized) claim that the vice presidency is “not worth a warm bucket of spit” and John Adams’s lament that the job is “the most insignificant office that ever the invention of man contrived or his imagination conceived.”

Okay, there are a few other items on my vice-presidential short list. Reporters and pundits should not pretend to know more than they do in portraying the inner thinking in the Romney camp. This is a moment when most big-name Republican consultants are either out of the loop or have an agenda like boosting a client whose image would be enhanced by a walk-on role in the vice-presidential pageant. So more phone calls generally lead to more conventional wisdom rather than to more insight. Add to the mix the deliberate self-serving leaks that may come from inside the Romney camp in order to signal to independent voters and GOP activists that the almost-nominee is considering women or Latinos or uncompromising social conservatives.

The only point of comfort for the political press corps is they are not the only ones who have blundered in the mug’s game of picking a vice president. Presidential nominees have not done that well either. It is worth recalling that the last three losing vice-president candidates were Sarah Palin (discredited), John Edwards (indicted) and Joe Lieberman (drummed out of his party). That should be enough to give anyone—reporter or political strategist—an intense feeling of humility during the next four months.

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Walter Shapiro just chronicled his ninth presidential campaign. He writes the “Character Sketch” political column for Yahoo News. Follow him on Twitter @WalterShapiroPD.