(In preparation for the 2008 political campaigns...)
besmirch \bih-SMERCH\ verb
: sully, soil
In order to besmirch the reputation of his opponent, Clay made sure to bring up the subject of the senator’s tax troubles during their first debate.
Since the prefix "be-" in "besmirch" means "to make or cause to be," when you besmirch something, you cause it to have a smirch. What's a smirch? A smirch is a stain, and "to smirch" is to stain or make dirty. By extension, "to smirch" came to mean "to bring discredit or disgrace on." "Smirch" and "besmirch," then, mean essentially the same thing. We have William Shakespeare to thank for the variation in form. Shakespeare's 1599 use of the term in Henry V is the first known appearance of "besmirch" in English.