Democratic front-runner Hillary ClintonHillary Diane Rodham ClintonGeorge HW Bush wears 'book socks' to Barbara Bush's funeral to honor her passion for literacy Obamas, Clintons to attend funeral of Barbara Bush Hillary Clinton to fundraise in DC for public charter high school MORE on Monday brushed aside Sen. Bernie SandersBernard (Bernie) SandersHannity snaps back at 'Crybaby' Todd: 'Only conservatives have to disclose relationships?' Chuck Todd lashes out at Fox, defends wife in radio interview Trump pressed Sessions to fire FBI agents who sent anti-Trump texts: report MORE’s (I-Vt.) earlier comment that her campaign is in “serious trouble,” saying she always expected a close race ahead of the Iowa caucuses.

“I always thought that this would be a close race. I’ve been around the track a few times,” Clinton said in a phone interview from Iowa on MSNBC’s “All In with Chris Hayes.” “It always closes. Iowa’s famously unpredictable.”

Clinton’s remarks come one day after a new NBC News-Wall Street Journal-Marist poll found Sanders maintaining his New Hampshire lead and closing the gap in Iowa.

"Suddenly Bernie Sanders is not a nice guy. That is not surprising when you have a Clinton campaign that is now in trouble and now understands that they can lose,” Sanders said earlier Monday.

The former secretary of State knocked Sanders for not releasing more details on his tax plan. On Monday, Clinton rolled out more components of hers, calling for an additional 4 percent surcharge on people earning more than $5 million per year.

“I have been laying out specific proposals over the course of my campaign, and I always said I’d be laying out additional elements of my tax proposal which I have,” Clinton said. “Sen. Sanders promised to be providing his tax plan before the Iowa caucuses yet I don’t think we’ve seen those.”

While Clinton wouldn’t weigh in on Sanders’s electability directly, the Democratic front-runner touted that she’s a “battle-tested” candidate.

“I know how to go up against the Republicans. There’s hardly anything that you and the voters don’t know about me, so there won’t be a lot of new information coming out, or new labeling coming out, and I think that's a big advantage,” Clinton added.

Jeff Weaver, Sanders campaign manager, responded to Clinton’s comments about the Vermont senator’s electability. “He has really been put through the ringer, so the suggestion that people don’t know who Sen. Sanders is is really not fair,” Weaver said on MSNBC.

Weaver pointed to recent polls that show Sanders faring better with independents and performing better in head-to-head match-ups with GOP candidates than Clinton.

“If Democrats want to win, you have to be able to win Democrats and you have to be able to win the lion’s share of independents,” Weaver added. “If you look at polling, he has consistently does better with independents than Secretary Clinton does.”

Weaver also argued that the Vermont senator’s campaign has attracted young voters and other groups who are less likely to vote. “We got to bring out a large amount of people who don’t traditionally come out,” Weaver said.

When asked about Sanders’s tax proposals, Weaver defended the Vermont senator’s tax plan, saying he’ll unveil more details before the Iowa caucuses, which will be held on Feb. 1.

“He has offered major pieces of his tax plan, and he will be offering up the part that deals with individual income taxes before the Iowa caucuses,” Weaver said.