Democrats have had a lock on the Massachusetts Congressional Delegation (as well as every statewide office) for some time now, with the exception of Scott Brown’s brief tenure as our junior U.S. Senator. To change this reality, Republicans (and independents) need to find voters who can be persuaded to change their party preference.

In short, they need to find swingers — or, less colloquially, swing voters.

So where do swing voters live in Massachusetts? The conventional approach to focus on the “bellwethers”: towns that have voted with the winner in past elections, regardless of party. But this misses an important nuance. Some towns may vote more or less intensely with their chosen party, swinging perhaps from a 50 point Democrat margin down to a 20 point Democrat margin, while never shifting from blue to red. This 30 point shift should be far more informative to a candidate’s targeting swing voters than a 6 or 7 point shift that takes a town from the Democrats’ column to the Republicans. Such a 30 point shift should mark a town as somewhere where ears are open, opinions are undecided — and votes are available for winning.

So where do these voters live? All over. The map below shows the towns that have shown the biggest shifts in overall margin over the last four gubernatorial and senate elections, with the darker shading indicating larger shifts. As is clear from the map, they are scattered around the state and follow no obvious geographic pattern.

Also notable, some of the areas with the biggest shifts are typically won by Democrats and others by Republicans. The map below shows the towns which Republicans and Democrats have won by an average of 15 points or better over the same four elections. Purple towns are those that were won by either party by a smaller margin.

Combining the two maps (below) shows that swing voters are available in Democrat towns, Republican towns, and in competitive towns.

So what does this mean for campaign strategy? First, it suggests that simply looking at who won each town is not an optimal strategy. Narrowing the gap in some towns will produce far more votes than flipping a town narrowly from blue to red. Losing by 20 is a lot better than losing by 50, and will move you closer to victory statewide. This approach also reveals the towns where each party can play offense — picking up voters in a town traditionally won by the other side — and also the places where they may need to play defense, shoring up support in towns they have won in the past but where the margin has been volatile. It may take more work, but finding and wooing these swing voters from unexpected places could pay dividends in the overall vote tally. Taken together, these data show that campaigns may benefit from a more sophisticated view of the electoral map going into the 2014 campaign.