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's campaign joined the growing pushback from 2020 Democratic presidential candidates to 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's Sunday meeting with North Korean leader Kim Jong Un.

"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," Biden spokesman Andrew Bates said in a statement.

Bates added that Trump has made "numerous concessions for negligible gain," during meetings with North Korea.

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Trump on Sunday became the first sitting U.S. president to cross into North Korea. He later announced the resumption of stalled nuclear talks with Pyongyang.

Democrats, including many of Biden's challengers in the presidential primary, have labeled Trump's visit a mere photo opportunity.

Biden's campaign also called out Trump's recent meeting with Russian President Vladimir Putin, where the presidents shared in a joke about "fake news" journalists.

Russian journalists have turned up dead over the years in Russia, a country that ranks low in terms of press freedom, according to the World Press Freedom Index.

"His 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 deliver real change for the American people," Bates said.