SCARBOROUGH KEEPS DIGGING…. Joe Scarborough’s on-air commentary is nearly always disheartening, but this morning was especially frustrating.

I can appreciate why the former far-right Republican congressman is feeling a little sheepish right now. Yesterday, Media Matters released a video showing reactions from conservative media personalities in April to a report from the Department of Homeland Security, warning law enforcement about the potential for violence from fringe radicals. The clip montage shows Scarborough not only dismissing the DHS report, but laughing hysterically at the very idea behind the report. He told his national television audience that DHS Secretary Janet Napolitano “has gone nuts.”

Of course, in light of the recent killings at the hand of some of these right-wing extremists, Scarborough’s laughter and dismissive attitude appears especially misguided now.

This morning, perhaps feeling a little embarrassed, Scarborough lashed out at Paul Krugman, and doubled down on his unjustified criticism of the DHS report from April.

On Krugman, Scarborough said:

“As somebody that has to sort through a lot of hate mail, a lot of hate email, a lot of viciousness. Paul Krugman’s name is attached to a lot of those emails. They use Paul Krugman as their shield for their left-wing hate. This is because Paul Krugman, like a lot of extremists on the right, they only see their side. They have a closed-minded world view. Paul Krugman uses this tragedy, uses this death to try to knock down his opponents on the right.”

Scarborough can’t (or won’t) address the substance of Krugman’s claims, so he finds it easier to equate the Nobel laureate with right-wing blowhards. As for the DHS report, Scarborough added:

“What upset most of us [about the document was] the fact not that they were targeting right-wingers, it’s that they were targeting veterans.”

Scarborough can keep saying that, but it doesn’t make it true. In our reality, DHS warned of a possible resurgence among extremist groups that “will attempt to recruit and radicalize returning veterans in order to exploit their skills and knowledge derived from military training and combat.” The document, initiated by a Bush administration official, relied in part on a 2008 report from the FBI, for the Bush administration, which raised identical concerns.

It would never happen, but instead of lashing out, Scarborough should either avoid the subject altogether, or apologize for his insulting behavior.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.