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A trio of polls released this week have found Vermont Sen. Bernie Sanders is gaining momentum in the race for the Democratic nomination

The former president's trip comes at a critical time for the campaign

Keene, New Hampshire CNN —  

Bill Clinton told CNN Wednesday that although he thinks his wife, Hillary Clinton, is the best candidate for president, he isn’t surprised the race is getting close.

A trio of polls released this week have found Vermont Sen. Bernie Sanders gaining momentum in the race for the Democratic nomination, including increasing his lead in the Granite State.

“I am surprised it didn’t happen 60 days ago,” said the former president. “Republicans always go after who they don’t want to be nominated in the primary. So, no, it didn’t (surprise me). I am surprised it didn’t happen sooner.”

Bill Clinton is on his second trip to New Hampshire, campaigning Wednesday along the Connecticut River for three events.

The former president’s trip comes at a critical time for the campaign, and Hillary Clinton and her team are responding to Sanders’ momentum with a series of endorsements and critiques against the Vermont senator.

Likewise, the tone of the campaign has grown markedly more combative in the last few days. Hillary Clinton has challenged Sanders on taxes, guns and health care in the last week, and Sanders has responded by charging that her campaign is getting desperate.

RELATED: Sanders may break health care pledge

“All they are doing now, as they should be doing, is talking about the differences in their positions,” Bill Clinton said while working the ropeline after a speech in Keene. “That is good. That is healthy.”

The tone of the campaign was made more stark on Tuesday when Bill and Hillary Clinton’s daughter, Chelsea Clinton, hit the campaign trail and knocked Sanders’ position on health care.

Chelsea Clinton charged that Sanders would “strip millions and millions and millions of people of their health insurance.”

“I don’t want to live in a country with unequal health insurance,” said the former first daughter after being asked about Sanders’ plan. “I don’t want to empower Republican governors. And I think that is what Sen. Sanders wants to do.”

Bill Clinton defended Chelsea on Wednesday in Keene in a conversation with NH1’s Paul Steinhauser.

“You know my daughter was asked a question about the relative health care. It’s what she does for a living. She teaches public health,” he said. “She’s actually read the plans. And there’s nothing wrong with what she did. She answered a question. And that’s what New Hampshire’s about, answering voters’ questions.”

RELATED: Sanders narrows gap on Clinton in national poll

During his remarks, Bill Clinton cast the former first lady as a hard worker who deeply cares about working and middle class people and would be ready to start as president on her first day in office.

He admitted, however, that he is a bit biased, something he said voters could call “the love discount.”

“Whatever I say about Hillary’s plan, you are entitled to give it the love discount if you want,” said the former president. “But I ought to get some credit for knowing something about how to run the economy.”