Well, probably a great many things, but especially . . . THEY CAN BOTH BE INDICTED BY A GRAND JURY.
But it will even be easier than than for Rove because he created and led an illegal conspiracy to expose an undercover agent of the CIA (and may have participated in the conspiracy as a principle himself).
The situation strongly implies that there were at least 2 different primary sources (since Matt Cooper's specifically released him, but Judith Miller's apparently did not do the same for her) and reason maintains there were at least 6 initial calls (the 6 reporters contacted: Robert Novak, Cooper, Miller, and 3 others), and 3 follow-up calls (Novak, Miller, Cooper). This is the minimum.
Since there were at least 6 initial calls and 2 different callers, Rove not only led it (doubling his charges) but it also means that there will be more than one indictment of the administration's top officials. Why? . . . Read on.
Scenario:
In order to make sure the story leaked properly, discrediting Wilson's Niger yellow-cake findings by implying he and his wife, Valerie Plame, had an agenda against the president from the beginning one person would have to coordinate the calling. (Of course he could have made calls as well.) Neither of the 2 or more should call the other's initial contact (that would seem too eager, perhaps a dirty trick). In addition, 4-5 others would have to know the story was true in order to confirm it, and they had to be encouraged to do so.
Who better than the master of such odious activity, Karl Rove? Perhaps Cheney (who would have felt responsibility in such a matter since it was the behest of his office that the CIA sent Wilson to Niger) used his clearance to discover this information and brought it to Rove at a meeting of the White House Iraq Group (see snippy's beautiful post in DU, link at bottom of this post). Then Rove would go into high gear, doing what he does best (I mean worst). He coordinated the callings, made sure there were the requisite secondary sources ready and willing to confirm (perhaps each having different details or a different slant).
Therefore, Rove may well be both a conspirator (a little RICO, anybody?), and the leaker of illegal information, AND we may have at least one other indictment handed down. Think of the possibilities! Rice, Cheney, Libby, Hughes (why the hell did she retire before?), Matalin, etc. Maybe even W. (But the more I think about it, I wonder how many real reporters wouldn't be suspicious of a call from Rove? He might be the primary source for the likes of Novak, but few others.)
But think about the above and then read snippy's lovely item backed up by a Washington Post article:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=102&topic_id=142863&mesg_id=142952