David Duke, a known white nationalist and ex-Ku Klux Klansman has unofficially endorsed Donald Trump for president, and that has many people wondering why Trump hasn’t spoken out against Duke’s support.

The New York Times reports that Trump came under fire on Sunday morning for not disavowing David Duke.

Donald Trump declines three chances to disavow David Duke https://t.co/Opf7os55Wo pic.twitter.com/qdaYjITFgd

— Huffington Post (@HuffingtonPost) February 28, 2016

While David Duke hasn’t made any kind of official endorsement of Donald Trump, he has called him “by far the best candidate.”

On his radio show in recent days, David Duke said of Trump, “Voting against Donald Trump at this point is really treason to your heritage.”

“Well, just so you understand, I don’t know anything about David Duke,” Trump said in an interview with CNN. “I don’t know anything about what you’re even talking about with white supremacy or white supremacists.”

This weekend, David Duke continued in his unofficial endorsement, post a lengthy piece about supporting Donald Trump on his Facebook page.

A spokesperson for Marco Rubio got after Donald Trump in light of David Duke’s support and his refusal to disavow that support.

Donald Trump declines to reject the support of ex-Klansman David Duke https://t.co/aVbdt6jdXO pic.twitter.com/UUHPluLKVM

— The New York Times (@nytimes) February 28, 2016

“If you need to do research on the K.K.K. before you can repudiate them, you are not ready or fit to be president,” Rubio rep Joe Pounder said.

Ted Cruz voiced his feelings, as well.

Really sad. @realDonaldTrump you're better than this. We should all agree, racism is wrong, KKK is abhorrent. https://t.co/dn2D74c5dl

— Ted Cruz (@tedcruz) February 28, 2016

“I don’t know David Duke,” Donald Trump reiterated on Sunday. “I don’t believe I have ever met him. I’m pretty sure I didn’t meet him. And I just don’t know anything about him.”

Hey everyone, meet the REAL Donald Trump, who enjoys Nazi support: Donald Trump Declines to Disavow David Duke https://t.co/iAKhlEwdRh

— Kara Swisher (@karaswisher) February 28, 2016

What’s your take on David Duke’s unofficial endorsement of Donald Trump? How do you feel about Trump having yet to speak out against it?

Could this be the downfall of the Republican presidential hopeful that Ted Cruz and Marco Rubio are no doubt praying for?