“The trouble with quotes on the Internet,” Abraham Lincoln once observed, “is that you can never know if they are genuine.”
Have you noticed how incorrect quotes often just sound right sometimes, more right than actual quotations? There’s a reason for that. Our brains really like fluency, or the experience of cognitive ease (as opposed to cognitive strain) in taking in and retrieving information. The more fluent the experience of reading a quote or the easier it is to grasp, the smoother it sounds, the more readily it comes to mind the less likely we are to question the actual quotation. Those right-sounding misquotes are just taking that tendency to the next step: cleaning up, so to speak, quotations so that they are more mellifluous, more all-around quotable, easier to store and recall at a later point. We might not even be misquoting on purpose, but once we do, the result tends to be catchier than the original.
On the other hand, in contemporary political discourse, it is probably wise to assume that any misquotation is deliberate.
A personal note: Since the old Movable Type days, I’ve had a sidebar feature called “It is written,” which yanks a quotation out of a text file. For some reason, most WordPress widgets offering rotating quotes expect you to store all that material in the database; the plugin used here does not, which is exactly why it is used here, inasmuch as that file has grown to about 160 kilobytes and roughly 2,000 quotes. Of those two thousand, I’ve had to go back and correct about 50, although the problem is more often misattribution than misquotation. I mention this because the piece to which I’ve linked contains one quotation I’d semi-improperly attributed: correct speaker, but incorrect rendering of his name. Of course, it’s since been fixed.