If he visits the Dome of the Rock. Things could get very interesting indeed.
"The Foundation Stone and its surroundings is the holiest site in Judaism. Though Muslims now pray towards the Kaaba at Mecca, they once prayed with the Jews towards the raised platform on which the Dome of the Rock stands. Though Muhammad changed the direction of prayer for Muslims after a spat with a Jewish tribe, both groups traditionally regarded the location of the stone as the holiest spot on Earth, the site of the Holy of Holies during the Temple Period.
http://en.wikipedia.org/wiki/Dome_of_the_Rock
Thanks for pointing out fact!
Topic: Will Barack Obama enter the Temple Mount in Jerusalem? - Streaming Audio Link