GOP presidential challengers Ted Cruz and Marco Rubio and Democrat Hillary Clinton desperately need breakthroughs in Iowa tomorrow to overcome expanding leads held by Donald Trump and Bernie Sanders in New Hampshire, a new Franklin Pierce University-Boston Herald poll reveals.

Trump has a massive 25-point advantage over his nearest rival Cruz while Sanders has grown his lead over Clinton to a 57-37 percent margin , according to the poll of likely Granite State primary voters conducted Jan. 26-30.

Poll results:

Summary: Franklin Pierce University-Boston Herald poll of Democratic voters

Tables: Franklin Pierce University-Boston Herald poll of Democratic voters

Summary: Franklin Pierce University-Boston Herald poll of Republican voters

Tables: Franklin Pierce University-Boston Herald poll of Republican voters

A surprise in the Iowa caucuses tomorrow could still shake things up in New Hampshire’s Feb. 9 primary, especially on the GOP side, where 44 percent of voters say they could still change their minds. One-third of Trump supporters say they haven’t made a firm decision.

But a dramatic shift in the Democratic race appears less likely, with 78 percent of likely primary voters reporting they won’t change their minds. That makes Clinton’s hopes for another comeback an even bigger climb, even if she beats the upstart Vermont senator in Iowa.

Trump now gets 38 percent of the vote in New Hampshire — up from 33 percent a week ago — while Cruz has stalled at 13 percent, according to the poll of 439 likely GOP primary voters.

Rubio and former Florida Gov. Jeb Bush are getting 10 percent, while Ohio Gov. John Kasich has dropped to fifth place at 8 percent, according to the poll. New Jersey Gov. Chris Christie, businesswoman Carly Fiorina and Kentucky Sen. Rand Paul are winning just 5 percent support, the poll shows.

Trump’s popularity has remained steady in the Granite State, with 56 percent of GOP voters saying they hold a favorable view of the billionaire business mogul.

The poll also reveals that the much-publicized endorsement of Trump by former GOP vice presidential nominee Sarah Palin has been no help. Six in 10 voters say Palin’s backing has had no effect on their decision, while 24 percent report it’s made them less likely to support Trump. Just 14 percent of voters say the endorsement made them more likely to back Trump.

The new Franklin Pierce-Herald poll shows Clinton has been unable to stop her stunning slide in New Hampshire despite her newly aggressive stance against Sanders. The Vermont senator’s 20-point lead is four points higher than the last Franklin Pierce-Herald poll conducted Jan. 20-24.

Just 72 percent of Granite State Democratic voters have a favorable view of Clinton, down 11 points since December, while 89 percent view Sanders favorably.

Despite Sanders’ popularity, 54 percent of likely Democratic voters in the new Franklin Pierce-Herald poll say they expect Clinton to be the nominee — though it’s down from a high of 74 percent in December.

With just 10 days left before New Hampshire voters go to the polls, a Clinton loss in Iowa could seal her fate in New Hampshire and hand her back-to-back losses in the crucial opening contests. In the last 40 years only one presidential candidate — Bill Clinton — has won the White House without winning Iowa or New Hampshire.

The Franklin Pierce-Herald poll also shows former New York Mayor Michael Bloomberg’s trial balloon of an independent candidacy hasn’t exactly resonated in New Hampshire. Nearly half of all likely Democratic voters say they wouldn’t vote for him in November, while 51 percent haven’t heard of him or have no opinion.

Developing…

­— joe.battenfeld@bostonherald.com