Conventional wisdom dictates that President Obama and former Massachusetts governor Mitt Romney will spend the next 78 days assiduously courting the sliver of voters — somewhere between 5 percent and 10 percent of the electorate — who call themselves political independents and insist they remain genuinely undecided about which candidate to support.

Elections are, after all, decided by the ideological middle; the two parties’ bases are already aligned behind their candidates, and the trick is to persuade enough of those centrist independents to side with your, well, side, to win.

Except, of course, when it’s not.

“The only thing undecided in this election are the TV anchors’ ties on election night,” said Dan Hazelwood, a Republican direct-mail consultant. “Both sides believe there is little chance for a dramatic shift in opinion, so that leaves trench political warfare as the default strategy. That means identifying and turning out your own supporters.”

Heaps of national polling would seem to affirm Hazelwood’s contention. Political polarization is at an all-time high, with even soft partisans already aligned behind either Obama or Romney. That has shrunk the middle of the electorate to single digits nationally. Simply put: There just aren’t that many people left for the campaigns to convince — no matter how much money (and it will be lots of money) the two sides spend between now and Nov. 6.

Given that political reality, there is a strong case to be made that the two campaigns should spend most of their time/energy/
money not trying to find and persuade independents and undecideds but rather trying to identify and rally their (already united) bases.

A base election — as opposed to an independents/undecideds/
persuadables election — is not unheard of. In fact, you need to go back only two elections to find one. In 2004, we had a president with middling approval ratings on the issue of the day (the war in Iraq) and an opposition party strongly energized to oust him. (Sound familiar?)

Knowing that winning over the middle — or voters even loosely affiliated with Democrats — was going to be next to impossible, President George W. Bush and his campaign strategists instead focused their efforts on their own party base. Everything — from Bush’s voter-identification efforts to the heavy national security messaging in his television ads — was targeted not at convincing persuadable voters that he should be their choice but rather at reminding Republican base voters why he was their guy.

It paid off. Although Bush lost independents to Sen. John F. Kerry of Massachusetts (he had won them against Al Gore in 2000), he improved his standing among self-identified Republicans by two points from 2000. That proved to be enough as Bush eked out a win with 286 electoral votes.

Seen through that base-election prism, the pick of Rep. Paul Ryan (Wis.) as Romney’s running mate makes perfect sense. Ryan is beloved among conservatives, while Romney, well, isn’t. If the Romney team has come to the conclusion that winning in November is more about making sure every Republican possible turns out to vote, then picking Ryan could well be a master stroke. (It’s less clear whether Ryan can help Romney appeal to independents if this election is, in fact, about that small number of persuadable voters.)

Celinda Lake, a Democratic pollster, acknowledged that 2012 is more a base election than a persuasion one but said that “it’s both.” She added: “Though undecideds are small, you still have 15 percent of Obama voters and 25 percent of Romney voters who would consider voting for someone else. That’s almost a quarter of the electorate that are undecided or swing.”

At the moment, Obama appears to be trying to run a “both/and” campaign — playing to the base with his public change of heart on gay marriage earlier this year and his executive order allowing young illegal immigrants to stay in the country, while also trying to reach fiscally conservative, socially liberal undecideds.

“I think you might say that the Romney camp is playing like it’s 2004,” said a senior Democratic official who spoke on the condition of anonymity in order to talk candidly about strategy. “But Team Obama is still in ’08 mode, particularly with independent women.”

Watch what Obama and Romney say on the campaign trail — and in their television ads — between now and November. Given the tiny number of genuinely undecided voters up for grabs, don’t be surprised if their messages start to sound more and more like appeals to their respective party bases as the election draws closer.