Some Things Never Change
"Some metaphors now current have been twisted out of their original meaning without those who use them even being aware of the fact. For example, toe the line is sometimes written as tow the line. "
(George Orwell, "Politics and the English Language")
"Lieberman has galvanized the left at a time when it's eager to flex its political muscle by attacking Democrats who don't tow the party line."
(Story in Time.com)
The Orwell essay, incidentally, is a classic, well worth reading if you are not already familiar with it.