Democratic presidential candidate Bernie Sanders has had a massive influx of campaign donations in the last few days - an apparent response to a barrage of attacks from 2016 rival Hillary Clinton, which the Vermont senator has called "mean-spirited and unfair and inaccurate," according to Politico.

"Thanks, Team Clinton," Sanders spokesman Michael Briggs told The Washington Post on Wednesday. "As of now, we are at about $1.4 million raised since yesterday when the panic attacks by the Clinton campaign began."

"We've gotten 47,000 contributions. We're projecting 60,000 donations. Even for our people-powered campaign, this is pretty darn impressive," he added. 

In recent days, Clinton has attacked Sanders on health care and gun issues. Sanders says that shows her team's concerns over his success in the polls, which indicate he could possibly beat Clinton in Iowa and put him well ahead in New Hampshire. Clinton has attempted to downplay the tight race.

"No I'm not nervous at all," Clinton insisted on the "Today" show on Wednesday, according to The Hill. "I'm working hard, and I intend to keep working as hard as I can until the last vote or caucusgoer expresses an opinion. I'm excited about where we are." 

Last week, however, Clinton campaign manager Robby Mook sent an email to supporters with the subject line "nervous," The Daily Caller reported. "I'm not trying to be dramatic about this situation (I swear! I'm really not!), but there's a situation developing in Iowa and New Hampshire that could change the course of this election," Mook wrote.

The Clinton campaign sent an email to supporters in New Hampshire appealing for donations, ABC News reported. "We're neck and neck in New Hampshire, and I need my best supporters like you with me," the email said. An email sent earlier in the week said: "Just four weeks from the New Hampshire primary the polls are (seriously!) tight."

The Clinton campaign boasted a $37 million fourth quarter to close out 2015, but Sanders was right behind with $33 million. For the year, however, there was a $40-million differential with $112 million for Clinton and $73 million for Sanders. 

Clinton leads Sanders in Iowa 46.8 percent to 42.8 percent, according to RealClear Politics averages. However, in New Hampshire, Sanders leads 48.8 percent to 42.6 percent. O'Malley is in a very distant third with 5.2 percent in Iowa and 3.0 percent in New Hampshire. Most recently, however, polls from Monmouth University show Sanders overtaking Clinton in Iowa, in a survey released on Tuesday, according to The Hill.