Barack Obama's finally clinched the Democratic nomination, but he'll probably look back on this stage of his campaign as the easy part. Among the issues he can expect to be pounded on in the months ahead is the one about who he knew and how he knew them.

Obama's already resigned from Trinity United Church of Christ to get out from under his associations with the Reverend Jeremiah Wright and Father Michael Pfleger -- which didn't help at all with such hostiles as the National Review. Tony Rezko made national news as an Obama associate when he was convicted Wednesday, and the GOP jumped in immediately with this video. And here's Michael Kinsley on "Obama's radical friends" Bill Ayers and Bernardine Dohrn. The former Weathermen "remain spectacularly unrepentant, self-indulgent, unreflective--still bloated with a sense of entitlement, still smug with certainty," in Kinsley's view, but he points out that if Obama has shown bad judgment in associating with them, so has  a "comically respectable list of Chicagoans and others -- including Republicans and conservatives." As Kinsley sees it, when Ayers, whose dad ran Commonwealth Edison and was on a lot of important boards, decided the revolution wasn't going to happen he simply went home and the establishment took him back into the fold.

Moral: Be careful who you meet on the way up. You'll meet them again on the way further up.