The Obama campaign is a threat to major centers of power in establishment circles, both Republican and Democratic. This is not because Obama's policies are so far to the left, they are actually relatively centrist in character. Its the politics that the powers that be fear, in particular the role of mass organizations such as MoveOn.org and activist networks such as Daily KOS.
Again it not necessarily because of the policies they advocate, but the politics they epitomize. The success of grassroots organizations on the left, even if now primarily restricted to the relatively young and intellectual, can serve as a template for a resurgence of organizing efforts within labor and amongst minorities. Obama, like FDR, must utilize these forces to catapult to power and in so doing will promote and nourish them, while simultaneously reigning them in. This same dynamic allowed progressives, including communists and other leftists, to enter into a broad coalition of forces that propelled the New Deal forward in the 1930s. The 1940s and 50s saw a wholesale purge of these forces from the Democratic Party which was facilitated by rampant red-baiting, tar and feathering all progressives with the stigma of "communist sympathies" and being pinkos. This same effort is now being unleashed on a reconstituted progressive movement and is being lead by reactionary forces in both the Republican and Democratic parties.
The continued focus on Rev. Wright's comments and the new attempt to associate Obama with the Weatherman Underground of the 1970s will continue to escalate. A Rovian smear campaign to brand Obama as a closet Marxist is already well underway. Gingerich is now intimating that Democratic activists are covert admirers of home-grown American terrorists. HRC slanders MoveOn.org partisans as thugs out to intimidate her supporters.
These are all classic tactics employed in the late 40s and 50s to discredit the progressive movement that had its roots in the upheavals of the 1930s and WW II. Those efforts were extremely successful and it's taken generations for a mature home grown progressive movement to re-emerge in this country. Unless this movement is fully cognizant of the dangers of red-baiting and the need to confront it head on I'm afraid history will repeat itself. It is not beyond belief that the pressures will built exponentially during the coming presidential race as desperate measures will be undertaken by corporate elites and special interests in both parties to preserve their power and influence.
Again they don't necessarily fear Obama's policies, they can be easily co-opted. What they fear and want to destroy and uproot are the independent actions of mass organizations that will have increased influence if Obama gains the presidency.
You ain't seen nothing yet!