The Democrats and the lone Republican hoping to defeat President Trump in 2020 were quick to react to the president's comments that he would be open to listening to information from a foreign country that could damage his opponent in the next election.

The Democrats and the lone Republican hoping to defeat President Trump in 2020 were quick to react to the president's comments that he would be open to listening to information from a foreign country that could damage his opponent in the next election. Several candidates used the opportunity to repeat for calls for impeachment, while frontrunner Joe Biden said it was a "threat to our national security."

In an interview that aired Wednesday, Trump told ABC News' George Stephanopoulos "there's nothing wrong with listening" if a foreign actor offered him information on a candidate.

Here are the candidates' reactions:

Joe Biden

"President Trump is once again welcoming foreign interference in our elections. This isn't about politics. It is a threat to our national security. An American President should not seek their aid and abet those who seek to undermine democracy." -- posted Twitter.

Bernie Sanders

"Well, Anderson, to tell you the truth, I'm not exactly shocked. I think we have a president who neither understand the constitution of the United States or respects the constitution. Somebody who doesn't believe in the separation of powers. And somebody who thinks he's above the law." -- said on CNN's Anderson Cooper 360.

Elizabeth Warren

"The #MuellerReport made it clear: A foreign government attacked our 2016 elections to support Trump, Trump welcomed that help, and Trump obstructed the investigation. Now, he said he'd do it all over again. It's time to impeach Donald Trump." -- posted on Twitter.

Kamala Harris

"He's the commander in chief and has a duty and a responsibility to the American people to be a defender if not the greatest defender of our democracy. But to quite the contrary, what we hear tonight is that he is yet again open to the idea of working with foreign governments to undermine the integrity of our election system. It's outrageous." -- said on MSNBC.

Beto O'Rourke

"When the President of the United States openly welcomes foreign help to win an election, he threatens the very core of our democracy. If we are to secure justice and ensure this never happens again, we must impeach him." -- posted on Twitter.

Amy Klobuchar

"This is inexcusable. The President of the United States just effectively gave permission to foreign agents to interfere in our elections. We need my Secure Elections Act and Honest Ads Act passed immediately. The 2020 elections are not secure. Disgraceful." -- posted on Twitter.

Cory Booker

"It's not 'oppo research' — it's foreign interference in US elections. That you would say this is disgraceful. That you would do it from the Oval Office (yet again) proves you're unfit for the office you hold." -- posted on Twitter.

Michael Benet

"My reaction is that this is weak and pathetic. This is what he has been doing since the beginning of his presidency even before he was president He said wikileaks if you're out there, send me the stuff. He said Russia, if you're out there, send me the stuff.

"Now he's actually president of the United States, and he's effectively inviting foreign interference into our election. He has never held Putin responsible for what Putin did. And he stood next to Putin and said I take his word for it.

"Every single Western democracy is under attack from Russia, and the President of the United States needs to be someone who stands up not just for America but for our allies as well, and he's failed that test again." -- said on CNN.

Seth Moulton

"The definition of collusion from the man guilty of obstruction." -- posted on Twitter.

Julian Castro

"After seeking and receiving the help of our adversaries to get elected in 2016, Donald Trump is now essentially calling for an open season on our 2020 elections. Once again, he's putting his interests above our nation's, and risking and the integrity of our elections." -- posted on Twitter.

Jay Inslee

"Let's be clear: Donald Trump is talking about conspiring with a foreign government to win an election — again. This is dangerous and un-American." -- posted on Twitter.

Kirsten Gillibrand

"It's time for Congress to begin impeachment hearings." -- posted on Twitter.

Eric Swalwell

"Let me make it clear for @realDonaldTrump, I will never take dirt from a foreign adversary — EVEN if it means beating someone as corrupt as you. *But Trump said every Congressman would take the help. So, every @HouseGOP member should have to answer this: is Trump right?" -- posted on Twitter.

Steve Bullock

"1-800-CALL-FBI

If he's telling foreign countries to dig up dirt on political opponents, it's no wonder he also made it easier to pour dark and foreign money into our elections. In MT, we banned foreign spending altogether. Together we can take that nationwide." -- posted on Twitter.

Republican William Weld