Senator Scott Brown’s decision to buck his party leadership in recent days on the “don’t ask, don’t tell’’ military policy and on a nuclear arms treaty has set off a new wave of anger among some of the activists who helped elect him — and renewed talk among conservatives that he might face a primary challenge. Some Tea Party movement leaders who dislike Brown’s votes acknowledge that the Massachusetts Republican has demonstrated his independent and pragmatic streak, and by doing so may strengthen his chances at reelection in 2012. No primary challenger has emerged, and it is unclear whether a...