It started in 2008 with a conversation between two friends at the Brookhaven at Lexington retirement community who wondered what they could do to help Barack Obama defeat John McCain.

By last month’s election, Grandmothers for Obama had grown into a national organization with nearly 1,000 members in 25 states and the District of Columbia. This summer and fall, its members wrote personalized postcards in support of their candidate to more than 100,000 older voters in swing states, according to Lexington resident Betsy Hatfield, the chief coordinator of the group.