Breaking down the Brown race - by the numbers

Incumbent congressmen such as Representatives Michael Capuano and Stephen Lynch, as well as former Kennedy chief of staff Gerry Kavanaugh, also continue to weigh campaigns, which would make the primary an even more fractious affair.

But following the departure from the race of Salem Mayor Kim Driscoll, who decided against running because of a young family, many backers of Governor Deval Patrick and Senator John Kerry are expected to gravitate toward Warren.

They argue as a city chief executive, Iraqi war veteran, and the only African-American in the field, Warren can compare favorably in November 2012 with the incumbent, Republican Senator Scott Brown.

The initial challenge for Warren is living up to those expectations. Then, if he does, he would face a stern test in unseating Brown, who has tried to maintain bipartisan support during the 15 months since he replaced the late Senator Edward M. Kennedy.

To hear some Democrats talk, though, it’s all but a slam dunk in 2012 for whomever emerges as their party's nominee.

They take a macro view of recent election results to make their case.

Brown shocked the political world in January 2010 by beating Democrat Martha Coakley to seize the seat held for nearly a half-century by Kennedy, a liberal Democratic icon.

The headline read, “Brown wins,” but the text told a more nuanced story.

Overall, Brown received 1.168 million votes, or 52 percent of the total cast. Coakley got 1.059 million, or 47 percent.

A total of 2.249 million votes were cast, with Brown getting 109,000 more than Coakley.

Yet when Brown runs next fall for re-election, seeking his first full Senate term, it will be 2012 — a presidential year.

Democrats take their comfort from the results during the last presidential year, 2008, when Democrat Barack Obama first appeared on the Massachusetts ballot.

In that election, Obama pummeled Republican nominee John McCain by a margin of 61 percent to 38 percent. Obama got 1.904 million votes, while McCain got 1.109 million. A total of 3.103 million votes were cast.

That is 854,000 more votes than in the Brown-Coakley special election.

In looking at those numbers, Democrats note that Brown received only 60,000 more votes than McCain, even when his special election was the lone contest on the ballot, even when independents broke in his favor, even when Coakley ran what she admitted was a botched campaign.

And if the presidential voting trend from 2008 carries over to 2012, when Obama will again be on the ballot, they see a better outcome for a Democratic Senate candidate.

They argue that if the extra 854,000 votes from the 2008 race were split by the same 61 percent-to-38 percent ratio seen in Obama's win over McCain, and then that vote split was added to the Republican and Democratic totals from the 2010 special election, “Coakley” would beat “Brown” by a margin of 1.580 million votes to 1.493 million votes.

As circuitous as that logic may be, some Democrats are warmed by the arithmetic. Others, though, take only cold comfort from it.

They note that Obama rode a historic wave, getting an additional boost in traditionally Democratic Massachusetts from voters who wanted to help elect the country’s first black president. Little more than two years later, even some of his fellow liberals are upset with decisions such as his military campaign in Libya.

They also note that Brown is a strong campaigner, good debater — and has proven adept at winning over independents with key votes since he was sworn in.

And they say that micro-level numbers are reason for alarm.

Patrick won the governor’s office in 2006, and re-election in 2010, with a traditional Democratic model: bigger margins in the urban, Democratic areas, and smaller numbers in the more Republican suburbs.

But if you examine a sample of two communities — Boston and Billerica — Republicans are buoyed by the trend.

In Billerica, a Merrimack Valley town, Obama won the 2008 election by a margin of 50 percent to 48 percent. He got 9,688 votes to McCain’s 9,274.

Yet in the 2010 Senate special election, Brown stomped Coakley in Billerica, 65 percent to 34 percent. He got 9,583 votes to her 4,972.

Last fall, there was a three-way race, but the general pattern held: Republican Charles Baker won Billerica with 54 percent of the vote, while Patrick garnered 33 percent and independent candidate Timothy Cahill received 11 percent.

Add Cahill's 1,642 votes to Baker’s 8,121 votes, and you get about 200 more votes than Brown received against Coakley. Patrick received 4,967 votes — five fewer than Coakley.

Is there a group of Democrats waiting to come out and vote for Obama again, or are those two recent numbers more predictive of Billerica’s 2012 vote than the 2008 results?

Meanwhile, in Boston, the state’s capital city, the vote distribution has been fairly static.

In 2008, Obama beat McCain 79 percent to 20 percent, or 184,320 votes to 45,248 votes.

In the 2010 Senate special election, Coakley beat Brown 69 percent to 30 percent, or 105,289 votes to 46,468.

Last fall, Patrick beat Baker 70 percent to 23 percent, with Cahill claiming 5 percent. Patrick received 113,668 votes, while Baker got 37,274 votes and Cahill got 8,638 votes.

In an increasingly polarized electorate, with history no longer at stake for Obama and Brown proving personally resilient in a state that elected Republican governors for a recent 16-year span (including Mitt Romney, who could be atop next year's GOP presidential ballot), some Democrats don’t see a slam dunk in 2012.

Instead, they envision a jump ball.

Glen Johnson can be reached at johnson@globe.com. Follow him on Twitter @globeglen.