Since I changed my voter registration to “unenrolled,” I have been curious who makes up the voters in that classification. It is the largest bloc of voter registrations in Maine.

Documented evidence is hard to find. I did discover in Maine voter registration data that the increase of “unenrolled” in our state between the 2004 and 2014 general elections matches the decrease in registered Republicans and Democrats. There is no research to explain the reason.

The best analysis is from Linda Killian, senior scholar at the Woodrow Wilson International Center for Scholars and journalism professor at Boston University, in her 2012 book, “ The Swing Vote: The Untapped Power of Independents.”

Killian pored through voter registration records across the country and interviewed voters. She grouped them in four categories to which she assigned names:

NPR Republicans: Killian wrote that they are fiscally conservative and socially moderate. Most prefer to register unenrolled because they believe the religious right wields party power disproportionate to its actual electoral effect. It has been my experience as a campaign consultant that this bloc tends to be more of a factor in presidential campaigns than at the state or local level.

America First Democrats: They are blue-collar patriots and socially conservative. If they themselves are not veterans, they have a son or daughter in uniform. (Thirty years ago, we called them Reagan Democrats.) Killian wrote that they register unenrolled because they think radicals, wealthy elitists and academics have taken over party power.

Facebook Generation: They are under 35, libertarian-leaning, educated and well informed on social media, but they distrust government and will not register by party because they blame Republicans and Democrats equally for the problems facing the nation.

Starbucks Moms and Dads: Killian wrote that this group is the hardest for a candidate to reach because their loyalties are to their families, immediate community of friends and associates and their own personal interests rather than to any political ideology or party. She wrote that they tend to approach voting in terms of “What’s in it for me and my family?”

To her four categories, I might add a fifth, which I would call Ideologues. These would-be voters on the left and right who have philosophical allegiance to smaller parties such as Peace and Freedom, Socialist, Libertarian, Constitution. However, they cannot register with those parties because they are not recognized in most states with ballot status.

Those categories combined comprise about 40 percent of the registered voters in this country. The major political parties ignore them at their peril because they are the swing vote in every general election.

In my campaign schools, I teach candidates that they cannot win a general election without strong outreach to independent voters. The registration numbers alone show one cannot win solely with the voters in one’s own party. In Maine, Democrat registrations are only about a third of the electorate, and registered Republicans are only 29 percent of voters.

The independents often vote in protest by withholding votes. Either they do not show up at the ballot box or, if they do, they take ballots to vote for president or the highest office on the ballot. They often leave blank offices where they dislike the candidates offered by the parties or they do not know enough about any candidate to cast a vote.

Maine makes it easy to analyze this effect on close races because the official results from the secretary of state lists “uncast ballots” for each office. I have studied legislative races where as many as 7 percent of those voting left the office blank and a shift of just a few points might have swung an election.

The challenge is to reach out to those independents, engage them and have a strong get-out-the-vote effort to turn out at the polls those who lean in your candidate’s direction. To achieve that, candidates should ignore the parties and retail themselves to voters on a very personal level addressing them on the voters’ terms.

Politicians should remember that voters do not want to be condescended to, and they have the clout to send them to defeat.

Vic Berardelli is the author of “The Politics Guy Campaign Tips – How to Win a Local Election” and a retired campaign consultant. An unenrolled voter, he is a former Republican State Committeeman and former member of the Republican Liberty Caucus National Board.