I mean, how can intellectually honest Objectivists support this guy with a straight face?
Playing factions against each other.
Obama is a far leftist, yes, that much is on his record. He’ll surely try to brutally expand government power over the economy, starting perhaps with oil or healthcare. He’ll raise taxes. He’ll further the cause of multiculturalism. He’ll try to do all that and worse.
When he does it’s very likely the GOP will oppose him for two reasons 1) partisan grounds (which is a pretty bad reason, but you can count on it) and 2) some Republicans still favor smaller, limited government.
Partisan grounds, though, are the most important reason. The GOP would largely support a president McCain in almost everything for the same reason; as it supported Bush on his prescription drug governmental expansion. McCain is a big government conservative. he will expand the powers of government, too, but in a more modest fashion than Obama. But he’ll do it nearly unopposed. democrats would press him for even more, if they press him for anything. So with Obama as president there is more oppposition in the right direction. it may even work.
That’s domestically (BTW if you favor an immigration bill, electing Obama nearly insures nothing will be done about it).
As far as foreign policies go, Obama will likely not pull the troops from Iraq prematurely (certainly not at once), but he likely won’t pressure Iran and other terrorist states. And there’s little GOP opposition can do to change that. McCain probably would conduct a more agressive policy towards Islamism, but he will be fiercely opposed by the Democrats and the the far left.
Like the Christian leaders who supported the formation of the state of Israel, hoping it would speed the Armageddon/Rapture/Second Coming/End of Days (whatever), are Objectivists trying to “force” an “Atlas Shrugged” scenario? 
I hope not. I see no hope of something like that doing any good even if it does happen. Reasons to be provided on request.
Regarding the Supreme Court, McCain would likely settle for an Anthony Kennedy type figure.