Opposition leaders have arisen, but the anti-Obama forces won't unite behind any of them. We're pretty sharply split over social/religious issues, and defense/Patriot Act type issues.
Go look at that thread about Jindal, that got locked a few days ago. Or any of the discussions we had about Palin. Those are the two major, potential leaders that have arisen recently, and about half of the anti-Obama crowd hates their guts. Rush Limbaugh is trying to be the opposition leader, and the Democrats seem to think he is. Similar division there.
Go back to the Republican primaries, where we were all split over the big-govt. social conservative (McCain), the "reformed" RINO social conservative (Romney), the not-so-big-govt. social conservative who waited until his moment had passed before even getting into the race (Thompson), the small-govt. anti-war, gold-standard, anti-PATRIOT Act social conservative (Paul), the sorta-big govt. social conservative (Huckabee), the big govt. social liberal (Guliani) and a few miscellaneous conservatives like Hunter.
We must resolve to agree to disagree on the divisive issues.