Well, Representative Hank Johnson, remember, there are no stupid questions, only stupid people.   To address your concerns: islands don’t stick out of the water because they’re buoyant.  They actually are mounds that go all the way from the ocean floor to the surface.  Like all areas of crust, they do, at least to some degree, “float” on the earth’s mantel, but you’d have to put a lot more than a few thousand marines on an area of crust to actually make it subside enough to start to “sink” into the mantel.

And that is why Guam won’t capsize.

Props to the admiral for maintaining a straight face and not making a wise crack.  I don’t think I could have done that.

Note: Apparently after this thing getting a great deal of media coverage, Hank Johnson responded that it was a joke. You can judge for yourself, but I don’t see any sarcasm or any joke-like setup (he sounds fairly serious about the size of the island, a lot of setup for a joke) to the question. Johnson has been known to go on some nonsensical ramble-sprees in the past, though none quite this bad.

Doesn’t look like a joke to me, and I certainly would not put it past a politician to actually believe that an island could tip over.