Trump is certain at some point to say outrageous and embarrasing things, which then become messes for the Romney team to clean up. He is all risk and no gain.
David Corn suspects that Romney is trying to prevent Gingrich from becoming the Tea Party candidate:
This shows that Romney cannot escape the gravitational pull of GOP craziness. The longer Gingrich remains in the race, the more Romney will have to pander to the Obama-hating extremists who make up much of his party.