Since the crisis in Ukraine began, the Russia scholar Stephen F. Cohen has cast himself in the role of the unbowed dissenter, whose sharp criticisms of America’s foreign policy in the region have earned him denunciations as “Putin’s American toady,” as The New Republic put it, and worse.

But Mr. Cohen is also a man of means, whose wife’s charitable foundation has donated large amounts of money to support Russian studies, which have been hard hit by declining government funding.

Now, his largess and his divisive reputation have collided, opening a rift in the main scholarly association covering the post-Soviet world and spurring charges that the polarizing politics of the Ukraine crisis are stifling free speech and compromising the group’s scholarly mission.

The affair began amicably enough two years ago, when Mr. Cohen and his wife, Katrina vanden Heuvel, the editor and publisher of The Nation, began discussions with the Association for Slavic, East European and Eurasian Studies, about ways to support research.