Rick Klein of ABC News appeared on CBN News' Faith Nation Monday to talk about Harris and the other Democratic candidates.

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Sen. Kamala Harris (D-CA) is officially on the campaign trail.

The 2020 Democratic presidential candidate held her first rally in her hometown of Oakland, California on Sunday. She reportedly drew more than 20,000 people to the event. That's more than former President Barack Obama had at his first rally back when he launched in his campaign back in 2007.

Harris has a long history of public service. She's a former prosecutor and served as California's first female attorney general from 2011 to 2017.

She was elected to the Senate in 2016. The junior senator has supported Medicare-for-all, legalization of recreational marijuana, sanctuary cities, passing a DREAM Act, and lowering taxes for the working and middle classes while raising taxes on corporations and the wealthiest top 1 percent of Americans, according to Wikipedia.

Appearing on CBN News' Faith Nation on Monday, ABC News' Rick Klein said Harris' event was a statement that belongs in the big leagues.

"No other candidate has even tried to put together a big outdoor rally like that," he said. "Doing it in her home base in Oakland says something as well."

"When you look at Harris, you've got a sterling resume as a prosecutor at a local level and the state level and then as United States senator," Klein noted. "Her multi-ethnic and multi-racial background I think is a big calling card. California is a big opportunity for fundraising and for building a base of support. And I think she's someone that's trying to signal from the start that she belongs there in the conversation among the serious candidates for president."

Klein said he's struck by a couple of Democratic candidates who got in the race early and a few who are staying out.

"Elizabeth Warren kind of got the campaign season started. We know her by reputation. She's a star in liberal circles. A lot of people thought she should have run four years ago and she decided not to," he explained. "We've seen the moves already by Harris, so I think she will be a first-year contender right off the bat. Senator Gillibrand from New York is another one."

"I'm also intrigued by some of these people who are waiting a little bit. Bernie Sanders is one of them. He had a huge following last time. We know it ended a little short for him. Will he be able to capture the same momentum?" Klein asked. "Vice President Biden, he's going to be a very big name when and if he makes the decision to do it. And then Beto O'Rourke, who comes off that losing Senate campaign with an unparalleled fundraising capability. He became a national and even an international Democratic superstar. He can wait maybe a little bit other than the others, because of the celebrity he derived from it."

Klein said he thinks the 2020 election will be a referendum on President Trump.

"But really it comes down to a thumbs up or a thumbs down on the president," he said. "He's the guy that on Election Day 2020 will have been in office for four years. How do people feel like its going? That is ultimately the biggest factor in a reelection race."