Does Novak Have to Squeal?

Eugene Volokh addresses a question I have been wondering about: can Robert Novak be legally compelled to reveal his source?
Eugene thinks (tentatively) yes, as the First Amendment claim that journalists sometimes make is not always upheld (Hey, I knew that: I saw Absence of Malice. Everything I needed to know about the law I learned from Sally Field…)
But the one factor I did not see in his analysis was the fact that Washington D.C. (which I presume would have jurisdiction, as I believe that is where Novak is based) has a “shield law” designed to protect journalists from having to reveal their sources.
I was able to confirm that the law exists, but unfortunately have not yet been able to find a link to the actual text.
I assume I am missing something fundamental here, but perhaps Prof. Volokh or someone else more legally qualified than I can clarify this point…
Update: Prof Volokh has kindly responded, stating:
The answer is no; the D.C. Code generally applies to proceedings in D.C. courts, and to D.C. prosecutors (plus possibly to civil actions brought under the diversity jurisdiction of federal courts, though I’m not sure how D.C. rules fit there). It would not apply, however, to Justice Department prosecutors — their actions in these matters are governed by the privileges set forth in general federal law, not the law of a particular state or of D.C., even if the prosecutors are physically located within that local jurisdiction.
However, reader Lead Balloons chimes in thusly in the comments:
Volokh commenting on your post stated that the D.C. shield law would only apply to a D.C. prosecution in the D.C. courts. I don’t know anything about the shield law. However, as a former AUSA in D.C., let me make two points: first, USDOJ is the local prosecutor in D.C. Secondly, there is no reason, other than politics, that the United States Attorney for D.C. could not investigate, and if necessary, prosecute, this case in either D.C. or federal courts. (That’s assuming the actions took place in D.C., seemingly a safe bet if the calls to journalists were made by White House officials.)
Curiouser and curiouser, say I! Seems that the question may well be more complicated than I had initially thought…