There was a commercial that the democrats did that flashed white letters on a black screen something like “who decides? democrats decide” but it disappeared in stages, like a powerpoint slide, and for a fraction the words “rats decide” was left on the screen—just long enough for people to grab a screen shot of it That was when we started calling them rats. I think this was in the Bush reign, maybe in 2004 against the lurch.
I think the “Democrats” got bigger and as it expanded off the screen “Rats” appeared for a couple of seconds. The rats howled about it, or no one would have noticed.
I think the ad you refer to was actually done by a GOP campaign, which is why the Rats threw a tantrum.