U.S. Sen. Bernie Sanders' once-formidable lead over Democratic rival Hillary Clinton in New Hampshire has shrunk to just 7 points, putting another Clinton comeback within reach two days before the pivotal first primary, a new Franklin Pierce University-Boston Herald poll reveals.

Longtime Republican frontrunner Donald Trump has also lost significant support – down to 31 percent – while Texas Sen. Ted Cruz moved up to 16 percent after his Iowa win, closely followed by Florida Sen. Marco Rubio at 15 percent, the poll of 433 likely GOP primary voters shows.

But the Republican contest could still undergo significant swings in the closing days, with 41 percent of likely primary voters saying they could still change their minds – an unusually high number in the final weekend of the primary battle.

Clinton's narrow Iowa victory has given her a major lift in the Granite State while Sanders now has reason to be nervous. The Vermont socialist senator was beating the former Secretary of State by a 57-37 percent margin right before the caucuses, but he now clings to just a 51-44 percent lead, according to the new Franklin Pierce-Herald poll of 407 likely Democratic primary voters conducted Feb. 2-6.

Clinton's favorable rating increased to 75 percent since Iowa and she also regained some of her aura of inevitability, with 61 percent saying she'll be the nominee while just 27 percent picking Sanders – a 13 point margin increase since last weekend.

Sanders continues to crush Clinton among New Hampshire independents and liberals, but the former first lady now leads her rival among registered Democrats by 51 to 46 percent.

But just 17 percent of New Hampshire Democratic voters now say they could change their minds, indicating there's unlikely to be major shifts in the closing days. The lack of volatility makes it even tougher for Clinton to overcome Sanders on Tuesday.

Trump's Iowa loss has made a major dent in his New Hampshire armor. His support dropped from 38 to 31 percent since the last Franklin Pierce-Herald poll just before the caucuses, while the number of Republican primary voters who believe the billionaire businessman will be the GOP nominee plunged from 57 to 39 percent.

Rubio is the hottest candidate in the GOP slugfest, according to the new poll conducted Feb. 2-6. His support grew from 10 to 15 percent since last weekend, while two-thirds of likely GOP voters in the Granite State now have a favorable view of him – easily the best marks in the pack.

A week ago, just seven percent of New Hampshire voters said it was likely he'd be the GOP nominee, but that number has skyrocketed to 23 percent now.

Cruz got just a modest bounce from Iowa, gaining three points, but the number of GOP voters viewing him favorably actually dropped from 57 to 48 percent, while his unfavorable marks shot up seven points to 46 percent.

Ohio Gov. John Kasich gained three points in the last week, and now stands in fourth place at 10 percent. Former Florida Gov. Jeb Bush continues to hold at 10 percent, while New Jersey Gov. Chris Christie stayed at five percent.

The high number of wavering voters in the GOP battle makes last night's debate even more crucial, with Rubio's shaky performance possibly slowing his momentum.

The survey was conducted by RKM Research and Communications and has a margin of error of 4.9 percent on the Democratic side and 4.7 percent for the Republican race.