Perry actually got in Obamas face and space in Texas awhile back. He tried to hand Obama himself a letter regarding the border. No other candidate has got right up and personal with Obama like Perry did.
And he's fighting federal agencies and has a redistricting case before the Supreme Court and Eric Holder has Texas' Photo ID languishing on his desk -- waiting is "approval."
Perry has been battling BIG government and winning many battles.
Now he wants to win the war.
And that is why I think Perry is the one that would intimidate Obama the most.
There's a lot to be said for physical presence and body language. Perry has it.