Something big changed between our March and June Suffolk University/Boston Herald polls for the New Hampshire Senate race: Libertarian Gardner Goldsmith is now on the ballot.

“A small leak can sink a great ship,” Benjamin Franklin once said. In politics a campaign can’t afford to leak votes away to other candidates, but that’s what’s happening to former Bay State Sen. Scott Brown’s campaign.

Recent public polls that showed the Brown vs. Jeanne Shaheen race closer than her current 10-point lead in our poll did not list Goldsmith as a candidate. And if you don’t think third-party candidates mean anything in New Hampshire, think again.

In our latest poll, even if Brown won all 9 percent of the undecided votes, he’d still trail Shaheen 49-48 with Goldsmith holding the precious remaining votes. Amazing. Goldsmith also got 4 percent of independents versus his 2 percent overall, which means the Libertarian is siphoning a greater share of independent voters away from Brown. Also, Goldsmith drew no registered Democrats, but 2 percent of registered Republicans, which comes off Brown’s tally, too.

Part of winning is finding your slice of the pie while your opponents split the remainder. If you look at this three-way race as incumbent vs. challengers, the advantage goes to the Democrat because there are now two anti-Shaheen options. With the surge of women elected in the Granite State over the past few cycles, the gender advantage goes to Shaheen.

Perhaps the only way to slice the pie bigger for Brown is to play off his Massachusetts roots versus the two longer time New Hampshire residents — but is that an advantage? Among former Massachusetts residents now living in New Hampshire, Brown tied Shaheen, 45-45. Among lifelong residents, Shaheen crushed him, 54 percent to 28 percent.

One option for Brown is to hope that President Obama’s numbers keep dropping, thereby dragging down all Democrats, including Shaheen. Currently, Obama’s job approval and favorabilities are at all-time New Hampshire lows and yet Shaheen still leads by 10. But what happens if the president’s numbers bounce back up?

Another Brown option is to ignore the Libertarian like he did in Massachusetts in his 2010 Senate race and go after Shaheen. But that would force Brown to go negative, and that means his 46 percent unfavorable rating could go dangerously higher.

Brown’s Republican primary opponents aren’t helping matters, either. Among voters of Brown’s closest opponent Bob Smith, 14 percent would vote for Goldsmith in the general election if Brown won the primary. An additional 41 percent of Smith voters would cast a ballot for Democrat Shaheen.

Talk about small leaks sinking a big ship.