Even if there was a legitimate reason to have him testify, can he really be subject to a subpoena?
Not saying that "if the president does it it's not illegal," but rather, isn't he the head honcho of those who have the power to enforce it? Maybe I'm getting my government powers mixed up, but it seems to me like calling a police station and asking the sheriff to arrest himself. (not even that, because there's someone over said sheriff that could do the arresting. There's no one over the president)
I'll be perfectly honest with you, I'm not sure if the issue has ever come up before. You're talking about subpoenaing the freaking POTUS man.... I don't know that this has been done and it's simply not something I've ever run across. It's entirely possible he might have
sovereign immunity. {to answer Pnx's post}
Devil's advocate for a second: Procedurally, when someone is subpoenaed they can usually fight it with a "Motion to Quash," which in English is them voiding the subpoena to have no legal effect. Simply it's getting out of it. There are certain things a motion like that has to have in it. I know what it is in Ohio, but it's different from state to state. If to beat the subpoena you have to have A B C and D in your motion, and you don't have all of those things (A B C and D), then your motion to get out of the subpoena may fail for technical reasons. If that's the case then they might technically have him. The link I posted to is the judge denying Obama's Motion to Quash (court filling to get out of the subpoena).
However, I highly doubt this has legitimacy. I mean really, you're talking about DOJ lawyers working directly for the POTUS man. Those guys are usually pretty good. The thought that they would make such a rookie mistake, while possible, just .... I don't buy it. Obama can pretty much hire any lawyer in the country, do you wonder if the ones he picked are any good?
Inherent skepticism aside, I find this hard to swallow.