Aficionados of the Etch a Sketch will recall a certain flaw in the toy: If you use it often, some of the lines drawn no longer disappear when you shake the device, instead leaving an indelible trace of where you have been.

This is the problem Mitt Romney is encountering: He is shaking the device, trying to erase impressions left during this year’s primary contest. But he just can’t shake away the image of Russell Pearce.

Pearce, the former Republican president of the Arizona Senate, is the author and self-described “driving force” behind S.B. 1070, that state’s law — endorsed by Romney — cracking down on illegal immigrants. Pearce told The Post’s Felicia Sonmez this month that Romney’s “immigration policy is identical to mine,” and he told reporters this week that Romney “absolutely” gave him the impression that he saw the Arizona law as a national model.