GREENVILLE, S.C. – One week after she formally announced that she is seeking the 2020 Democratic presidential nomination, Sen. Elizabeth Warren, D-Mass., campaigned in South Carolina on Saturday, bashing President Donald Trump's newly declared national emergency and attacking "corruption" Washington.

Warren is one of many Democrats bidding for the White House in the 2020 presidential election and out on the campaign trail Saturday.

At her rally last week in Lawrence, Massachusetts, the senator touted her support for progressive politics with a backdrop of Everett Mills, the site of a workers strike 100 years ago led by women and immigrants that boosted workers rights.

Here are four takeaways from the Greenville, South Carolina, event Saturday:

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Standing-room crowd turned out

Most of the seats set up inside the West End Community Development Center were filled shortly after the doors opened at 10 a.m., an hour before Warren spoke. Her campaign said about 800 people came to the event.

The crowd included Kelly Reaves and her 16-year-old son, Jordan, who traveled to Greenville from Hendersonville, North Carolina. Kelly Reaves said she supports Warren's positions on health care, climate change and women's rights.

Warren's two problems with Trump's emergency declaration for a border wall

In an exclusive interview with The Greenville News, part of the USA TODAY Network, the Massachusetts senator said she has "two problems" with Trump's decision to declare a national emergency to justify the allocation of federal dollars to build a wall on the Mexican border.

"The first is I don’t think this is an emergency. The facts don’t support it. And the second is I don’t think it is legal. That’s why there’s already a challenge in court. Ultimately of course the courts will determine that," Warren said. “I think he’s headed in the wrong direction here.”

Addressing another issue, Warren said that "a trade war by tweet as the president has done, it makes no sense. It doesn’t make us build a stronger economy or help workers here in the United States."

Washington 'works great' for the wrong interests

After talking about her family's financial struggles when she was a child growing up Oklahoma, Warren went on an extended riff about how Washington "works great" for powerful special interests.

"It works great for giant drug companies – just not for people who are trying to fill a prescription. It works great for giant oil companies that want to drill everywhere – just not for people who see climate change headed our way," she said.

"It works great for investors in private prisons – just not for the people whose lives and the communities that are torn apart. Yeah, Washington works great for those who have money. And we need to call that out what it is: corruption, pure and simple."

Sharing the stage in South Carolina, a key state in the 2020 race

Warren, who was scheduled to travel to an event in Georgia later Saturday, was not the only Democratic presidential hopeful stumping in South Carolina. Sen. Kamala Harris of California held a town hall in Charleston on Friday and traveled to Columbia for another campaign event on Saturday.

South Carolina will be the site of the first Southern primary in the Democratic race for president next February, making it a key player in the race, analysts say.

Follow Kirk Brown on Twitter @KirkBrown_AIM