Bernie Sanders might be Donald Trump’s best friend in New Hampshire.

Sanders’ surge in the first-in-the-nation primary state isn’t just hurting Hillary Clinton in the Democratic race; it’s a significant threat to a number of Republicans hoping they can lure independents to support them in the GOP primary.


Many of these independent voters, according to recent polling, are feeling the Bern.

Voters registered “undeclared” make up a plurality, nearly 44 percent, of people on the New Hampshire rolls. That’s significantly more than registered Democrats (26 percent) or Republicans (30 percent). And unlike other states, New Hampshire allows independent voters to select one party’s ballot on Primary Day without changing their voter registration.

A new study of undeclared New Hampshire voters — conducted this past weekend by the MassINC Polling Group for WBUR-FM, the Boston NPR affiliate — finds roughly a third of those undeclared voters say they haven’t decided which party primary they’ll choose. And where those voters end up has a major effect on the candidates at the top of each field: Sanders and Trump.

Among independents surveyed by MassINC, Sanders by far has the best favorability ratings. And while Sanders and Trump are both native New Yorkers making populist appeals in their respective races, registered independents don’t have nearly as charitable a view of the real-estate magnate.

But the GOP candidate most threatened by Sanders’ momentum isn’t Trump. It's Ohio Gov. John Kasich, whose standing in some polls has swelled in recent weeks in large part due to support from independents. Kasich needs those voters to pick up a GOP ballot rather than vote for Sanders in the other elections.

“I would bet that a lot of those people who were going on the Democratic side — if they were going on the Republican side, they would vote for Kasich,” said Patrick Murray, director of the Monmouth University Polling Institute, which released new surveys for both parties in New Hampshire last week.

According to crosstabs of that poll provided to POLITICO, Kasich — who tied Ted Cruz for second place overall, well behind Trump — ran stronger among independents and new registrants participating in the GOP primary (18 percent) than among registered Republicans (11 percent). The difference for Trump between Republicans (33 percent) and independents (32 percent) was negligible.

Among Democrats, Sanders leads Clinton among registered Democrats, 50 percent to 42 percent — but has a wider advantage, 58 percent to 34 percent, among independents.

It’s a pattern seen in other surveys. Kasich is the only candidate — other than Sanders — with net-positive favorability ratings in the new WBUR/MassINC survey of independents. Sanders’ favorability is sky-high: Fifty-nine percent favorable versus 32 percent unfavorable. Kasich’s: Forty percent favorable versus 34 percent unfavorable.

The other candidates fare far worse among independents. Clinton (33 percent favorable/59 percent unfavorable), Marco Rubio (29 percent/54 percent), Chris Christie (31 percent/52 percent) and Trump (28 percent/65 percent) are all well underwater.

MassINC Polling Group president Steve Koczela stressed that these independents are not a monolithic bloc but rather a fragmented group that includes voters who lean toward both parties and a middle group that vacillates between the two in the primary.

Koczela said he pulled a random sample of registered independents who voted in both 2000 and 2008 — the last two cycles in which both parties held contested primary battles — and found that roughly a third of those voters pulled ballots in different primaries in those two elections.

In fact, the independent bloc as a whole moved between the two elections, Koczela said. More than 60 percent of independents voted in the Republican primary in 2000, when Arizona Sen. John McCain upset then-Texas Gov. George W. Bush. But in 2008, when Clinton came from behind to defeat Barack Obama, more than 60 percent of undeclared voters participated in the Democratic primary.

“The frequency of switching ballots is quite high,” Koczela said. “It’s not a stretch to think there are voters on the fence who consider candidates on both sides.”

But there are also registered independents who function otherwise as partisans, Koczela said, despite their registration. The most conservative of those voters are backing Trump and Texas Sen. Ted Cruz, while the most liberal are mostly behind Sanders.

Some important caveats on the data: In most polls, the slice of independents who say they’ll participate in one primary or another is a relatively small sample. And a University of New Hampshire poll — conducted for CNN and WMUR-TV and released Wednesday evening — showed Trump doing slightly better among independents, and Kasich a little better among Republicans. (Though among Democrats, the poll — which showed Sanders with a massive, 27-point advantage overall — has Sanders at 50 percent among registered Democrats and 70 percent among independents.)

Ultimately, Koczela said, Sanders’ popularity among independents could cut both ways for the GOP field: If independents who usually move between the two parties cast their ballots for Sanders, that hurts Kasich and other moderate candidates on the Republican side — and boosts Trump, who leads by 16 points to 20 points in the most recent reliable polls.

On the other hand, if Sanders continues to pad his lead over Clinton in the state, undeclared voters who are currently on the fence could choose to vote in the more compelling Republican race if they think the Vermont senator has the Democratic primary in the bag.

“What we don’t know is which contest is still going to be interesting in three weeks,” Koczela said. “The best thing that could happen to John Kasich is that Bernie Sanders opens up a huge lead.”