I see that even the return address on the Leahy letter envelope, even though it's the same as that on the Daschle letter envelope, was separately written. Look at the final line, that with Franklin Park and the zip code. On the Leahy letter, it slopes much more downwards.
Of course, the address to the senator had to be separately written, because Leahy and Daschle have different addresses. It will be interesting to see whether the letters are identical (as the Brokaw and NY Post letters are), so that they are presumably the result of mechanical copying with a xerox machine or the like.
Thanks for the analysis! I'm hoping the copy was made on a cheap fax/copier that uses film ... the image would be on the take up roll!