If polls are to be believed, Hillary Clinton's once commanding national lead over Bernie Sanders appears to have evaporated in a matter of days -- pointing to trouble ahead for the former secretary of state as voters cast their ballots Tuesday in Sanders-friendly New Hampshire.

Two recent national polls show Sanders closing the gap against Clinton.

A recent Reuters/Ipsos poll shows Clinton leading Sanders 48-45 percent.

And a Quinnipiac University poll from Friday showed Clinton leading 44-42 percent.

Both polls were taken since the Iowa caucuses.

The Vermont senator also has led in virtually every New Hampshire poll going into Tuesday’s primary, after narrowly losing to Clinton last week in the Iowa caucuses. 

See the Fox News 2016 battleground prediction map and make your own election projections. See Predictions Map →

While state polls are by far better indicators going into each individual primary, the national polls help gauge the candidates’ broader appeal. Over the past several months, Clinton has at times led the national polls by more than 30 points – contributing to her “front-runner” label even as she faced tight races in Iowa and New Hampshire.

Clinton, interviewed on MSNBC Monday night, said she knew this wasn’t going to be easy.

“I always knew that Senator Sanders [has] been in public life next door for 25 years; he's [in] the Congress for that long, he had a tremendous amount of familiarity and a sense of really belonging in the area,” she said. “So, I always knew this was going to be hard. I feel good about the campaign we waged here. I think we have an uphill battle. We're going to battle it until the last votes are counted and we're going to turn around and head off for the next contest.”

The polling may still be in flux. A Rasmussen poll also taken right after the Iowa caucuses showed Clinton retaining a double-digit lead.

But Sanders may be heading for a big win in New Hampshire Tuesday night, if he can hold off Clinton, who has gotten tougher on the Vermont senator in recent days – as her husband Bill Clinton also ratchets up his attacks.

“When you’re making a revolution, you can’t be too careful about the facts,” Clinton said at a Milford, N.H., event Sunday, a swipe at Sanders’ call for political upheaval.

He followed up Monday at an event at Manchester Community College, accusing Sanders of demonizing anyone who disagrees with him.

“We can’t get in a place where we’re so mad that we demonize anyone who is against us, where we can’t have an honest discussion about health care, where anyone who is on the other side is part of a mystical ‘establishment,’” Clinton said. 

At a rally Monday in Derry, N.H., Sanders continued to slam Clinton for the help she’s getting from super PAC donations. On Twitter, Sanders said if voters show up in large numbers, he’s got New Hampshire locked down.

“If there is a high turnout tomorrow, I think we are going to win. I urge you all: Come out and vote. #VoteTogether,” he tweeted.

The Quinnipiac poll of 484 Democrats was taken Feb. 2-4, and had a margin of error of 4.5 percentage points. The Reuters/Ipsos poll of 512 Americans was conducted Feb. 2-5 and had a margin of error of 5 percentage points.