Several 2020 Democratic presidential contenders ― including Sens.Kamala Harris (D-Calif.) and Cory Booker (D-N.J.) and former Vice President Joe Biden ― slammed President Donald Trump on Wednesday, for saying that he would accept information from a foreign government on his political rivals.

Harris, who is one of two dozen Democratic nominees vying for the presidency, called Trump a “national security threat” in a tweet late Wednesday.

Biden said that Trump was “once again welcoming foreign interference in our elections.”

Booker took a shot at Trump’s comments, saying: “It’s not ‘oppo research’ ― it’s foreign interference in US elections.”

Sen. Elizabeth Warren (D-Mass.), in turn, renewed her calls to impeach Trump.

And former Housing and Urban Development Secretary Julián Castro said Trump was “essentially calling for an open season on our 2020 elections.”

In an interview with ABC News’ George Stephanopoulos, an excerpt of which aired Wednesday, Trump said he would listen to information from a foreign government on his opponents in the 2020 presidential election. The president also suggested that he wouldn’t need to alert the FBI.

When asked whether he would accept information from a foreign entity like China or Russia on a political rival or instead call the FBI, Trump replied, “I think maybe you do both.” He then added he would call the FBI only if he “thought there was something wrong.”

“I think I’d want to hear it,” Trump said. “It’s not an interference.”