Is there a limitation to how many tickets you can be on for PotUS?

[JTsyo]

Would it be possible for them to run on 2 tickets?
ie Obma/McCain and McCain/Omba
One has VP other as P

 

[nageov3t]

the democratic party would have to nominate McCain as their VP candidate.
the republican party would have to nominate Obama as their VP candidate.

I'm not sure which is less likely, but I can't see it being illegal.