UPDATE: Matt Brooks, executive director of the Republican Jewish Coalition said he did not appreciate Gaetz citing the RJC to defend Johnson's views about the Holocaust:

“This organization is deeply troubled by the comments from Charles C. Johnson, and it is incredibly important for the congressman to acknowledge he is a Holocaust denier and has extensive writings that attest to that and that it was wrong to bring him to the State of the Union,” Brooks said. “We are are deeply troubled by any inference that our organization believes otherwise.”
Gaetz had cited a founding member of the RJC, Alfred Balitzer,  who wrote him to say he had never heard Johnson deny the Holocaust.
Let’s close the loop on Florida’s highest profile congressman, northwest Florida Republican Matt Gaetz, inviting a racist, white nationalist to President Trump’s State of the Union speech last week. Gaetz this morning for the first time said he regrets giving a ticket to notorious alt right activist Charles C. Johnson.

"It was a poor decision on my part not to do better vetting. I won't do that again. But I think that labeling Mr. Johnson a denier of the Holocaust has been met with skepticism from people who have dedicated a substantial portion of their lives to Holocaust remembrance," Gaetz told the Pensacola Morning News radio show, invoking the Republican Jewish Coalition and Alan Dershowitz.

The Holocaust denial label stems from the transcript of a since-deleted Reddit  Q & A with Johnson:

what are your thoughts on the Holocaust, WW2, and the JQ (anti-semitic conspiracy theory speak for The Jewish Question) talk in general? 

I do not and never have believed the six million figure. I think the Red Cross numbers of 250,000 dead in the camps from typhus are more realistic. I think the Allied bombing of Germany was a war crime. I agree with David Cole about Auschwitz and the gas chambers not being real. I read the German War (highly recommend), Bloodlands, Mein Kampf, and all of David Irving. I'm more or less of the view that the war was an outgrowth of the efforts of communism to spread itself throughout the world. I also believe that the fears of German extermination were not misplaced, especially in light of the Ukrainian famine. But I support Israel as a Jewish state and Zionism as a concept.

Johnson, who is suing Twitter for banning him for life,  had claimed the transcript was fake, but on FaceBook over the  weekend he acknowledged  the post "does reflect statements I made but it does not reflect my views on the Holocaust."

He did not mean what he said, Johnson said, but was actually conducting a stealth campaign to test Reddit's commitment to free speech:

Over the last few years I have financed a project studying the various tech companies and their commitments to free speech against fake hate speech. I began this process several years ago when I joined a group of likeminded individuals committed to getting Ellen Pao fired from Reddit over her reluctance to embrace free speech. In that instance as in this one anti-Semitic language trended to the top of Reddit and lead ultimately to her firing.

Got it? Not a Holocaust denier. No way.