Washington (CNN) President Donald Trump may have made history Sunday in taking 20 steps into North Korea, but for some 2020 Democrats, the event was nothing more than a "photo op" that hurt America more than it helped.

Trump and Kim Jong Un's meeting merely elevated the image of a dictator, a number of presidential hopefuls contended, while others argued it would net no tangible results -- like getting rid of North Korea's nukes.

Here's what the 2020 Democrats had to say after Trump became the first sitting president to enter the hermit nation.

Elizabeth Warren

Sen. Elizabeth Warren of Massachusetts said Trump shouldn't be "squandering American influence on photo ops and exchanging love letters with a ruthless dictator ," in a tweet.

"Instead, we should be dealing with North Korea through principled diplomacy that promotes US security, defends our allies, and upholds human rights," the Massachusetts Democrat wrote.

Kamala Harris

Sen. Kamala Harris of California criticized Trump for meeting with the dictator of a country that the US has repeatedly sanctioned and lambasted for its human rights record.

"This President should take the North Korean nuclear threat and its crimes against humanity seriously," Harris posted on Twitter, adding, "Our security and our values are at stake."

Joe Biden

A spokesman for former Vice President Joe Biden told CNN in a statement, "President Trump's coddling of dictators at the expense of American national security and interests is one of the most dangerous ways he's diminishing us on the world stage and subverting our values as a nation."

Andrew Bates said in the statement Trump "fawned over Kim Jong -un -- to whom he's made numerous concessions for negligible gain -- joked with Vladimir Putin about our election security and 'getting rid' of journalists, and even expressed sympathy for Turkey buying Russian missiles."

Julián Castro

Julián Castro said Trump "haphazardly" meeting with Kim raises the dictator's profile and is "strengthening him across the world," while giving the US "nothing."

"That is a problem," Castro told CNN's Brianna Keilar on "State of the Union" on Sunday.

"It's all show, it's all symbolism, it's not substance," the former secretary of Housing and Urban Development said, adding Trump "keeps telling us one thing, but the reality is another."

Castro said he supports diplomatic conversations, but said Trump "seems bent on approaching this very erratically, very haphazardly" and pointed to how the meeting was put together "at the last minute."

Trump extended what he claimed was a spontaneous invitation to Kim in a Saturday morning tweet for a handshake at the DMZ.

"If Chairman Kim of North Korea sees this, I would meet him at the Border/DMZ just to shake his hand and say Hello(?)!" Trump wrote.

Castro added Sunday: "I'm not quite sure why this President is so bent on elevating the profile of a dictator like Kim Jong Un when Kim Jong Un has not lived up to his promise from the first summit."

Amy Klobuchar

Sen. Amy Klobuchar of Minnesota said she supports discussions, but said "toughness is just not saying things by tweet, toughness is results and standing true to our country."

"The President will meet with him, that's fine, it's always good to talk to people when you're dealing with something so important as nuclear weapons, but then we have no clear path and nothing come out of it," she told Keilar Sunday on "State of the Union."

"I don't think we know if it works until there's results," she said, saying Trump has in the past announced summits with Kim and "nothing really comes out of it."

JUST WATCHED With 20 steps, Trump made history in North Korea Replay More Videos ... MUST WATCH With 20 steps, Trump made history in North Korea 02:26

Klobuchar said the US wants to see the reduction of North Korean missiles and denuclearization, "but it is not as easy as just going and you know, bringing a hot dish over the fence to the dictator next door."

She called Kim "ruthless" and said Trump has to have a "clear mission and clear goals," which she said he has not yet shown, in order to make progress.

Bernie Sanders

Sen. Bernie Sanders of Vermont said Sunday on ABC's "This Week" that he didn't have an issue with the President negotiating with US adversaries. Sanders cautioned, however, that the meeting wasn't much more than a "photo opportunity."

"We need real diplomacy," he said. "What's going to happen tomorrow and the next day?"

Sanders explained his dismay in the Trump administration's handling of the State Department and diplomacy with other countries.

Trump has "weakened the State Department," Sanders said. "If we're going to bring peace to this world, we need a strong State Department, we need to move forward diplomatically, not just do photo opportunities."

More than two years into Trump's presidency, key positions remain vacant throughout his administration, including at the State Department.

The Trump administration has repeatedly attempted to slash the State Department's budget , and State has struggled to fill overseas posts due to factors including the hiring freeze implemented under former secretary of state Rex Tillerson and reduced appropriations.

The Vermont senator wished Trump would sit down with adversaries in the Middle East and in the Persian Gulf.