Sanders on Sunday dismissed charges from Hillary Clinton's campaign that he has flip-flopped on gun-control as "a lot of nonsense," and said her campaign was "getting defensive" because her lead in the polls is shrinking.
"We are closing in in Iowa, we're doing really well in New Hampshire, so I think in the next two weeks you're gonna see a lot of nonsense being thrown around," he said on NBC's Meet the Press.
A new NBC News/WSJ survey of Democrats nationwide, released on Sunday, gave Clinton a 25-point lead on Sanders, but her prospects are far less rosy in the first two voting states.
The most recent NBC News/WSJ/Marist poll of likely New Hampshire Democratic primary voters, out at the start of the month, showed Sanders up four percent. The same survey of likely Iowa Democratic caucus-goers had Clinton up by three.
The tightened polling has sparked a battle between the the two campaigns in the final weeks before Iowans head to the polls, and the Clinton campaign has seized on Sanders' more moderate positions on gun control as a tool to blunt some of the momentum he's gained.
The Vermont Independent voted in 2005 to give gun manufacturers immunity from prosecution for crimes committed with the guns they sold, and repeatedly stood by that vote in comments on the trail. But on Saturday, he came out in support of a bill that would rescind that immunity. Clinton's top campaign aide on Saturday called it a "debate-eve conversion" in a tweet, and Clinton outright called it a "flip-flop" on CNN's "State of the Union" on Sunday.
But on "Meet the Press," Sanders insisted it was "not really" a shift and that it had been consistent with his comments months ago that "I was willing to rethink [about the issue]."
"We have rethought," he said. "I like that bill. It makes some good changes, and we will be supportive of it."
Clinton's allies have also targeted Sanders for his vote for a provision that would've allowed people to purchase guns before a background check was fully completed, within a day of starting the buying process. A tweaked version of that loophole allowed the Charleston church shooter Dylann Roof to purchase the gun he used in the June shooting.
Asked about the issue on Sunday, Sanders said he hoped there was no need to "politicize" the church shooting, and charged that Clinton was getting "defensive" because of his gains in the polls.
"I think the reason that the Clinton campaign is getting defensive is they see that we have the momentum. They see that the issues that we are talking about — a disappearing middle class, and almost all new income and wealth going to the top 1 percent; a corrupt campaign finance system, where people like Secretary Clinton can raise millions of dollars through Super PACs; those are the kinds of issues that they don't want to discuss," he said.
But Clinton dismissed questions over the strength of her campaign in an interview on "Meet the Press" shortly before Sanders'. She said that she "always knew this was going to be close," and expressed confidence in her position on voting day.
"I feel very good about where we are, but we're going to keep working until the very last caucus is decided on February 1," she said.
This article first appeared on NBCNews.com.