JMM:

If the president’s aides were using RNC emails or emails from other Republican political committees, they can’t have even the vaguest claim to shielding those communications behind executive privilege.

Yeah.  I don’t see anyway around that.

UPDATE:  The Carpetbagger raises two other issues regarding the White House staffs use of RNC emails:

There’s still the Presidential Records Act to consider. The PRA mandates thorough record-keeping, which Rove & Co. apparently hope to avoid. The law isn’t supposed to be optional.

and also:

As Laura Rozen explained, there are security concerns to consider. Rozen noted earlier this week, that the White House is a huge electronic surveillance target and by announcing that they’re not using their official email accounts anymore, foreign intelligence agencies might “become curious about the 95% of the government’s business that Karl is lobbing outside the system.” Rozen added today:

A reader who has a security role at a federal agency writes, “On the issue of using outside/unofficial e-mail address from official sites, the CIO at [redacted] has expressly forbade the practice for security reasons as it is all too easy to put sensitive information in an e-mail. … Needless to say, hearing that the WH does not mandate that practice and lets [Rove] do 95% of his e-mailing from a blackberry, presumably with access to an unofficial address, is quite shocking. Still find it absolutely amazing that his clearance has not been revoked.”

Good points.