Story highlights I think the secretary's people are getting nervous about the kind of energy and enthusiasm our campaign is bringing forth," Sanders said

Clinton said Saturday she welcomes the competition in the Democrats' primary process

Altoona, Iowa (CNN) After four months on the campaign trail marked by big crowds, growing support and rising poll numbers, Bernie Sanders is closing the gap in Iowa and around the country as he chases Democratic front-runner Hillary Clinton.

And on Saturday, he openly suggested that the Clinton campaign is "getting nervous."

"Don't tell anybody. I think what they know is that four months ago, when I entered this race, if you look at the polls, I was in 3 to 4%. Vast majority of the American people didn't know who Bernie Sanders was, they didn't know what my ideas were, and in last few months, we have amassed huge amounts of enthusiasm and huge amounts of energy," Sanders said. "So obviously, I think the secretary's people are getting nervous about the kind of energy and enthusiasm our campaign is bringing forth."

Clinton seemingly took a subtle swipe at both Sanders and Donald Trump , the GOP front-runner, in an interview with NBC's Andrea Mitchell on Friday -- though she didn't name them.

"I think you can come with your own ideas and you can wave your arms and give a speech. But are you connecting with and really hearing what people are either saying to you or wishing that you would say to them?" Clinton said.

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