[Nevermore]

The president gets sued all the time. When the suit involves his duties as president then the Justice Department acts in his defense.

But this is NOT a suit about what he has done as President; this is a suit about his qualification to BE President. He is not who he purports to be.
Suppose an individual were to be an Impostor, posing as Pres. BO, having knocked off the Original. If someone discovered that and sought to have the court remove the Impostor from office, would you expect DOJ to defend him? This is no different, IMO.

[Non-Sequitur]

But this is NOT a suit about what he has done as President; this is a suit about his qualification to BE President. He is not who he purports to be.

But it still pertains to his duties as president. And as such, the Justice Department provides the defense.

Suppose an individual were to be an Impostor, posing as Pres. BO, having knocked off the Original. If someone discovered that and sought to have the court remove the Impostor from office, would you expect DOJ to defend him? This is no different, IMO.

Until the impostor is proven to be the impostor then he/she is presumed to be president.