Democrats running for president on Sunday panned President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE for stepping onto North Korean soil, then meeting with the nation's leader Kim Jong Un Kim Jong UnPelosi knocks Trump over refusal to commit to peaceful transfer of power Satellite images indicate North Korea preparing for massive military parade South Korea warns of underwater missile test launch by North Korea MORE as ill-conceived and a waste of American bargaining power.

Trump made history on Sunday by becoming the first sitting U.S. president to set foot in North Korea. He and Kim then met for a surprise negotiation session that lasted about 50 minutes on the South Korean side of the Demilitarized Zone.

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The president hailed the meeting as an important breakthrough that will improve future communication between the two countries, and asserted it was an achievement that former President Barack Obama Barack Hussein ObamaObama warns of a 'decade of unfair, partisan gerrymandering' in call to look at down-ballot races Quinnipiac polls show Trump leading Biden in Texas, deadlocked race in Ohio Poll: Trump opens up 6-point lead over Biden in Iowa MORE had grasped at futilely.

Democrats immediately went on the attack Sunday morning, painting the meeting as an amateur move unlikely to produce any meaningful agreement on North Korea’s nuclear weapons and ballistic missile testing program.

A spokesman for former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE, the democratic frontrunner, hit Trump for “coddling” dictators, citing his chummy meetings with Kim and Russian President Vladimir Putin Vladimir Vladimirovich PutinPutin nominated for Nobel Peace Prize Navalny released from hospital after suspected poisoning Ex-Trump national security adviser says US leaders 'making it easy for Putin' to meddle MORE.

“President Trump’s coddling of dictators at the expense of American national security and interests is one of the most dangerous ways that he’s diminishing us on the world stage and subverting our values as a nation,” said Biden campaign spokesman Andrew Bates.

The spokesman said Trump’s “conduct reinforces that we urgently need a president who can restore our standing in the world, heal relationships with key allies Trump has alienated, and delivered real change for the American people.”

Sen. Elizabeth Warren Elizabeth WarrenHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Democratic senators ask inspector general to investigate IRS use of location tracking service MORE (D-Mass.), who is alternating between second and third place in national Democratic primary polls, also weighed in.

“Our President shouldn’t be squandering American influence on photo ops and exchanging love letters with a ruthless dictator. Instead, we should be dealing with North Korea through principled diplomacy that promotes US security, defends our allies, and upholds human rights,” she tweeted.

Sen. Bernie Sanders Bernie SandersThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Bernie Sanders: 'This is an election between Donald Trump and democracy' The Hill's 12:30 Report: Trump stokes fears over November election outcome MORE (I-Vt.), who is running neck and neck with Warren, charged that Trump’s visit “weakened the State Department.”

“The concern here is his incredible inconsistencies. I have no problem with him sitting down with Kim Jong-un Kim Jong UnPelosi knocks Trump over refusal to commit to peaceful transfer of power Satellite images indicate North Korea preparing for massive military parade South Korea warns of underwater missile test launch by North Korea MORE in North Korea or any place else. But I don’t want it simply to be a photo opportunity, the whole world’s media was attracted there,” he said on ABC’s “This Week with George Stephanopoulos.”

“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,” he said.

Trump drew fire from other Democrats as well, including Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.) and Julián Castro, who are running lower in the polls.

Klobuchar expressed skepticism that Trump’s meeting would lead to anything substantive and criticized him for taking an overly simplistic approach to a foreign policy problem that has challenged the United States for years.

“We want to see a denuclearization of the Korean peninsula, a reduction in these missiles but it’s not as easy as just going and, you know, bringing a hot dish over the fence to the dictator next door,” Klobuchar said on CNN’s “State of the Union.”

“This is a ruthless dictator and when you go forward, you have to have clear focus and a clear mission and clear goals,” she said.

She pointed to an earlier meeting between Trump and Kim in Singapore last year that failed to change North Korea’s testing of ballistic missiles in violation of international law.

“We’ve seen a history here, especially in this case where Donald Trump announces these summits and nothing really comes out of it,” Klobuchar said.

Castro, a former Obama Cabinet official, said Trump appeared to lay little groundwork for his meeting with Kim.

"It's worrisome that this president erratically sets up a meeting without the staff work being done. It seems like it's all for show, it's not substantive," Castro, the former secretary of Housing and Human Development, said on ABC's "This Week."

"I am all for speaking with our adversaries, what's happened here is this president has raised the profile of a dictator like Kim Jong Un and now three times visited with him unsuccessfully because he’s doing it backward," he said.

He noted North Korea has not kept its pledge to the Trump administration to disclose its nuclear stockpile inventory.

Obama’s former acting CIA director Michael Morell backed up the candidates’ criticism, warning on CBS’s “Face the Nation” that “we’re paying a price” for meeting Kim on his home turf.

“This comes at a very high cost. This gives Kim Jong Un a lot of legitimacy. This is gold for him politically at home and in the world,” he said.

Longshot White House hopeful Rep. Tim Ryan (D-Ohio) on Sunday compared Trump's visit with Kim in the hermit nation to British Prime Minister Neville Chamberlain meeting with Adolf Hitler.

"They talk about historic moments. This is historic, him going to North Korea is like Chamberlain going to talk to Hitler," Ryan said on CNN's "Reliable Sources."

"I mean, this guy was lobbing missiles into the Sea of Japan just a few weeks ago and the president is going to talk to him? I mean, are you kidding me?” Ryan added of Kim.

Long-shot presidential candidate Andrew Yang Andrew YangDoctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls Buttigieg launches his own podcast MORE broke from the pack, however, by praising Trump’s meeting.

“Anything that improves the political climate on the Korean peninsula and engages North Korea on its nuclear program is a good thing,” he tweeted.

Updated 4:05 p.m. Chris Mills Rodrigo contributed to this report.