The issue I could see with this is that political groups would have a very strong incentive to get around this and would try to push the limits of it. For example, if advertising about specific candidates is made illegal, groups might make ads promoting or attacking certain political positions instead, as a proxy for the candidates. If you make political advertising for anything illegal, even if not mentioning a specific candidate, then it would get even more thorny, because almost anything can be a political issue. For example, some right-wing political group might try to claim that gay marriage is a political issue and that any depiction of it in media is therefore advertising a stance on it, and sue anyone showing such on those grounds to try to silence people they don’t like.

Finally, political groups might just buy ads using organizations based outside the country, or use the advertising money instead on hiring people to go on social media and shill for their preferred candidates or positions, having the same effect as advertising without actually running ads.