WASHINGTON (Reuters) - U.S. candidates running for the 2020 Democratic presidential nomination on Sunday criticized President Donald Trump’s latest overture to North Korean leader Kim Jong Un, saying the leaders’ meeting lacked substance and elevated a ruthless dictator.

The Republican Trump became the first sitting U.S. president to step into North Korea on Sunday, drawing on his penchant for showmanship and surprise to pull off talks with Kim in the Demilitarized Zone that divides the two Koreas.

The meeting, at Trump’s last-minute invitation, drew praise from some including Pope Francis as a step toward peace. Critics called it a publicity stunt and said Trump wasted an important symbolic move when there has been little sign that North Korea has taken meaningful steps toward denuclearization.

A number of Democrats vying to replace Trump in the White House in the 2020 election said there was nothing wrong with talking to U.S. adversaries including Kim. This round of talks however, they said, should have followed intense preparations and substantive progress by North Korea on the nuclear issue.

“Our President shouldn’t be squandering American influence on photo ops and exchanging love letters with a ruthless dictator,” U.S. Senator Elizabeth Warren said in a Twitter post.

Her Senate colleagues Bernie Sanders and Kamala Harris called the event a “photo-op.”

Sanders said he did not fault Trump for meeting with Kim, but asked: “What’s going to happen tomorrow and the next day? He has weakened the State Department. 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.”

Trump has raised the profile of a dictator by meeting with Kim three times now with nothing to show for it, according to Julian Castro, U.S. housing secretary under President Barack Obama, and former U.S. Representative Beto O’Rourke.

North Korea has not lived up to commitments made in previous summits with Trump and intense preparations should be have been made before the leaders met again to ensure progress, they said.

“He’s doing it backward,” Castro said.

A spokesman for former Vice President Joe Biden said Trump was “coddling” dictators at the expense of U.S. national security.

North Korea launched missiles into the sea just last month, U.S. Senator Amy Klobuchar noted, showing the need for the United States to go into such talks armed with a clear mission and clear goals.

“It is not as easy as just going and bringing a hot dish over the fence to the dictator next door,” she said.

The candidates spoke on CNN’s “State of the Union,” ABC’s “This Week” and CBS’ “Face the Nation.”

(The online version of this story corrects the spelling of Jong in the lede)