21.   After all, the Manhattan A-bomb project in New Mexico during World War II was riddled with Russian spies, some still undiscovered, historians say.

22.   But a Texas historian said the letters may be worth that much to collectors of signed originals, but not to scholars.

23.   But Biblical historians say the tradition of pilgrimages on the west side grew up as a matter of convenience.

24.   But Carter ran out of time and the issue was then dropped, historians say.

25.   But even the strictest Old World racial caste systems broke down in the wilds of the Caribbean, historians say.

26.   But as haulers-in-chief, historians say, the first family was in good company.

27.   But he failed to remove wet clothes that afternoon and by early the next morning, his throat had swollen, making it hard to breath, historians say.

28.   But historians say that when the British executed the rebellion leaders, public opinion changed immediately.

29.   But historians say they still know very little about this golden age.

30.   But it is not the monumental victory it might have been, military historians say.