In D.C.’s own rendition of manifest destiny, our suburbs seem to be expanding with all the vigor of well-watered kudzu. It’s how DCist imagines the old horror standard The Blob, if it were retold by John Cheever: the mucilaginous mass slowly gorges on pastoral countryside, dusty antique shops, and quaint Main Streets, leaving only Bed, Bath, and Beyond in its wake. While taking a look at the political implications of these population shifts, the Post…