I say pass this now and have it apply now. If the present person in the Oval office is legal, he shouldn’t have any problems with such legislation, nor should his supporters.
If such a law was passed it would be important to get a “Strawman” to start the litigation immediately, otherwise the 2012 election would just start the process and it would take 2-3 years to wend its way though the state courts and the US Supreme Court.
If the present person in the Oval office was legal, he would not have gone to great expense to block the disclosure of his real birth certificate and then sealed his other records, as well.
Big "if".