Recent historical precedents for a Scott Brown win are obviously few, since the Bay State hasn’t elected a Republican to the Senate since the Nixon administration. In an excellent piece, Steve Kornacki diagrams the victory strategies of Massachusetts’s three most recent GOP statewide office-holders, all of them governors.

Unfortunately, none are strict analogues for Brown’s situation. Republican governors William Weld and Paul Celluci, who ran Massachusetts in the 1990s, faced Democratic opponents that were odious to progressives (Weld’s opponent John Silber) and unions (Celluci’s opponent Harshbarger) on policy grounds. Coakley may have run an awful campaign but, aside from the suggestion that Catholics don’t belong in emergency rooms, she hasn’t really run afoul of Democrats on their bread-and-butter issues. (Though, as Brown’s chief strategist tells Bob Costa at Bay State Report, voters across the spectrum seem to be fired-up about national security, which would definitely break for Brown.)

Brown’s best bet is probably to emulate Mitt Romney’s 2002 gubernatorial run, in which Romney pitched himself as a counterweight to unchecked Democratic power. Like Romney, Brown will have to rack up large margins of victory around Boston’s I-495 beltway, home to independents and recent arrivals from out of state. He is already polling well in three historical bellwethers in the area, and dominates independents across the board.

But in a state where Democrats outnumber Republicans three to one, there is no question Brown will have also have to garner a non-trivial number of them for his cause to win. There is some evidence that he is doing that: last week’s Suffolk poll showed Brown with at 53/45 lead among voters in union households. As Politico notes, the answer to whether Brown can hold these voters will come from working-class Irish Catholic towns along the South Shore, places like Braintree and Quincy where Obama faired worse than Kerry.

On the other side of the ledger, Coakley will need big urban turnout and at least a 65,000–80,000 edge over Brown in Boston/Cambridge to win. And it wouldn’t hurt if the electorate that shows up to vote is both skewed female (she holds an 4–5 point advantage among women) and credulous enough to believe the rape attack ads against Brown.

Turnout is expected to be inordinately high for a special election, with predictions — including one from the secretary of the commonwealth — cohering around the 40–50 percent and 2–2.2 million marks.

The last minute get-out-the-vote effort by Coakley has been massive, employing a battalion of as many as 3,500 volunteers, many dispatched by the AFL-CIO and SEIU, to take to the fields and man phone banks. (By contrast, a Brown official has said the campaign had only about 500 volunteers as of the weekend).

But anecdotal evidence, here and elsewhere, suggests that turnout is especially high in the suburbs — Scott Brown strongholds.

There is, of course, still another model Scott Brown could follow to victory. Namely, the Scott Brown model. What we are seeing today is no less than unprecedented, and so historical antecedents are of limited use. As the Brown strategist told Bob, you might as well “throw out the rule book” and wait for the tabulations.