I saw it again today, this time in a comment on an article on a political website. It referred to reporters who mindlessly "tow the administration's line."
Um, that should be "toe the line."
A lot of people who don't know the origin of the phrase picture someone pulling a rope, cord, or some other "line"--"tow the line"--as a way of working for whomever the "line" belongs to. Thus, if the administration has a "line"--i.e., a "party line"--then those who side with the administration help to pull it ("tow" it) along.
The phrase "toe the line" is equivalent to "toe the mark," both of which mean to conform to a rule or a standard. The Oxford Dictionary of Word Histories (Oxford: Oxford Univ. Press, 2002; ed. by Glynnis Chantrell) says, "The idiom toe the line from an athletics analogy originated in the early 19th century" (514).
The specific sport referred to is foot-racing, where the competitors must keep their feet behind a "line" or on a "mark" at the start of the race--as in "On your mark, get set, go!"
So one who "toes the line" is one who does not allow his foot to stray over the line. In other words, one who does not stray beyond a rigidly defined boundary.