US Sen. Cory Booker says Gov. Chris Christie is the field's most underestimated 2016 candidate

Don't count Chris Christie out.

That was the message Monday from Democratic U.S. Sen. Cory Booker, who said he believes New Jersey's Republican governor is the "most underestimated" presidential candidate in the crowded 2016 field.

"I think he's one of the more talented political people that are out there today," said Booker, speaking at a lunch event held by the news organization Politico in Newark.

Booker and Christie have long been friends despite their political differences. Christie's campaign has been struggling to gain momentum as he faces a field of more than a dozen other Republican candidates, including several current and former governors. But Booker said he believes Christie's chance of winning the nomination is "better than people think it is."

Booker, speaking during a wide-ranging interview, also bemoaned the state of the region's transportation infrastructure, which he described as in "crisis." New Jersey Transit and Amtrak trains suffered major delays last week that infuriated commuters — adding to frustrations that Booker shares.

"We should be ashamed of ourselves," he said. "We inherited the best infrastructure on the globe from our grandparents ... and we've taken that inheritance and squandered it."

Booker said he's been in discussion with New Jersey and federal officials, including Christie, about the need to build a new tunnel under the Hudson River and sounded somewhat optimistic about potential progress.

"I think we're going to have a constructive conversation, all of us, about a larger plan," he said, adding that he felt the social media storm from angry commuters had helped to draw attention to the situation.

The former Newark mayor has also been talked about as a potential vice presidential contender, but Booker said he's more interested now in supporting Hillary Rodham Clinton, the front-runner for the Democratic nomination, who he said has the clearest pathway to the White House.

"I think the vice presidency is not a focus and not important right now," he said.