But now, as the two men anticipate tough general-election battles in the fall, their paths are beginning to diverge. Brown, who will face a difficult reelection fight, probably against Harvard professor and former Obama administration official Elizabeth Warren, is working hard to define himself as a “Massachusetts moderate,” hoping to build support among Democrats in the deeply blue state.
Romney, meanwhile, has been working equally hard to escape that label, which his rivals for the GOP presidential nomination have used as a slur against him during the primary campaign.
The likely result is that Brown will be forced into a delicate dance in the coming months to distance himself from a political mentor and his state’s other most prominent Republican politician. It is a twist of irony unique to Massachusetts but one that could hold broad significance to the marquee race.
Recent polls show Brown leading Warren, who has drawn national support because of her outspoken warnings about the excesses of Wall Street. But the November contest is widely considered a tossup, and the electoral math is difficult for Brown.
In the small world of Republican Massachusetts politics, the links between the two campaigns are especially close. Gail Gitcho, Romney’s communications director, once served that role for Brown. Colin Reed, Brown’s chief spokesman, used to work for Romney.
Robert Maginn, chairman of the state Republican Party, who is responsible for helping to get Brown reelected and boosting Romney’s chances if he becomes the party’s presidential nominee, is a Romney ally and a former board member at Bain Capital, which Romney founded.
And both campaigns employ strategist Eric Fehrnstrom to craft essentially opposite messages for the candidates — helping Romney argue that he is a reliable conservative and Brown present himself as an independent centrist.
“It might be easier for Brown if one of these other candidates were the nominee,” said Todd Domke, a Massachusetts-based Republican strategist. “Then he’d just distance himself totally and run as an independent. But he can’t plausibly do that entirely from Romney. The links between them are inextricable.”
Fehrnstrom referred questions to Brown’s campaign manager, Jim Barnett, who said that the campaigns’ overlap is “deep inside baseball” and that Massachusetts voters will support Brown’s moderate approach over what he said would be an overtly partisan turn by Warren.
“I don’t think voters care about the hired help,” he said of the shared consultants. “Massachusetts voters are very sophisticated, and they recognize that Scott Brown is an independent Republican and his own person.”
With movie-star good looks and an everyman image, Brown won the 2010 special election against Attorney General Martha Coakley, in part by rallying a small group of tea party activists behind his promise to oppose Democratic efforts to reform the health-care system.
Since his election, he has sometimes angered those core supporters with his willingness to cross party lines and vote with Democrats on key issues, an increasingly rare trait in Washington as moderates such as Sen. Olympia J. Snowe (R-Maine) prepare to depart.
Some observers say he will use those efforts to present himself to the Democratic state as a different kind of candidate than Romney.
“Scott Brown has to sell himself as very different from Mitt Romney,” said Jeffrey Berry, a political science professor at Tufts University. “He will have to convey that he’s one of the few people left in American politics who’s willing to cross party lines and be that moderate voice so missing in American politics right now.”
Brown was an early endorser of Romney’s presidential campaign. But a Romney victory in the Massachusetts Republican primary Tuesday was a forgone conclusion — he took more than 72 percent of the vote — which meant that Brown did not need stump for him in in the state in recent weeks.
With the Senate in session, Brown was in Washington on Tuesday and did not attend Romney’s Super Tuesday rally in Boston.
As many as 800,000 more residents are expected to vote in November than took part in the special election that Brown won. Many of them are Democrats who support Obama’s reelection.
To win, Brown probably would have to persuade several hundred thousand people who vote for Obama to cross party lines and support him for the Senate.
With those voters in mind, he is pitching his independence — in contrast to Romney, who has been trying to frame his tenure as Massachusetts governor as “severely conservative.”
“I don’t worry about the party line. I don’t get caught up in petty fights,” Brown told a crowd in Worcester in January as he began his reelection effort.
But in the face of an effort by Warren to nationalize the race, Brown may find it more difficult to distance himself from his fellow Massachusetts Republican than he would from a different nominee.
Warren — who will compete in a primary for the Democratic nomination in September, although no Democrat has mounted a serious challenge — will say that Democrats who support Obama should vote against Brown. Her argument is that a vote for Brown would help Republicans take over the Senate and thwart the president’s agenda — Brown and Romney are no different, she says.
Last week, for instance, her campaign highlighted Brown’s support for a controversial amendment in the Senate that would allow employers to avoid providing insurance coverage for contraception if they hold moral objections to it.
Democrats thin that Warren, who helped create the new Consumer Financial Protection Bureau, is the perfect messenger in a campaign that they think will revolve, nationally and in Massachusetts, around restoring a balance between the middle class and corporations and the wealthy. A well-known figure on the left, she is likely to receive support from Democrats nationwide, although Brown starts with a significantly larger campaign war chest than Warren.
“The easiest way to tie somebody to something is with their own words. Scott Brown’s endorsement of Mitt Romney, his long history, their shared staffers and advisers — there’s a close tie between these two guys,” said John Walsh, chairman of the state Democratic Party.
But there are some areas in which Brown could easily draw distinctions with the former governor: He supports abortion rights, favors stem-cell research and backed ending the military’s “Don’t ask, don’t tell” policy for gay service members.
Enraging many conservatives, Brown supported the Dodd-Frank financial legislation, which all of the Republican presidential candidates have vowed to repeal.
And while Romney struggles to overcome a reputation as a stiff campaigner uncomfortable with his wealth, Brown has an appealing personal story of overcoming a hardscrabble childhood. He famously drives a pickup truck and wears a barn coat.
When Romney awkwardly told a group of voters in Michigan last week that his wife, Ann, drives “a couple of Cadillacs,” a spokesman for presidential rival Newt Gingrich invoked Brown’s name to mock the former Massachusetts governor.
“Just doesn’t have the same Scott Brown ring to it,” R.C. Hammond tweeted.
Some Massachusetts strategists said Brown’s plan to focus on state issues might be made easier, ironically, by the lack of a competitive presidential race in the state. Because Obama is expected to win Massachusetts easily, all the electoral excitement in the state will focus almost exclusively on the Senate contest.
“Massachusetts voters understand the presidential election is not in doubt in the state. The focus will be on the Senate,” said Rob Gray, a Boston-based Republican strategist who worked for Romney when he was governor. “It could be awkward, but Scott will do what he has to do to distance himself. And depending on the dynamics of the race, it may come to transpire that he does not have to distance himself that much.”