I dont think it will be a big problem they usually dont give as much weight to other grad grades. As long as you do well in your post bacc i dont see it being a problem. Although, make sure that your grades are low because you just dont care about law school and not because the work is too hard. If you dont do well in the postbac youve blown your last chance at a US med school.
I wouldn't tell them that your law school grades are low because you "judt dont care about law school." Saying that you didn't care about law school yet spent a lot of time and investment getting into law school shows poor judgment. You're going to show up in the interview and say, yeah, my low GPA in law school was because I just didn't care about law school, not because I didn't work hard. Wow, that's poor judgment again.
They can easily infer that, well, heck, if this guy didnt care about law school, there's a possibility (however small) that he might not care about medical school once he got in. I mean, there's so many qualified applicants out there that medical schools don't need to take a "risk" on you to find out whether you will or will not do well. Unfortunately, law school is more comparable to medical school than a grad degree in philosophy, in the sense that you are going up against the best and the brightest and if you couldn't hack it in law school, it's the same crop of overachievers in medical school, you might not be able to hack it in medical school. You should be the best possible applicant you can be and any doubts or question marks on your record should be mitigated. At the end of the day, a low GPA does not instill confidence.
It's like going on a job interview saying oh I got fired from my last job because I just didn't care, not because I didn't work hard. It's a hard argument to make and prevail on.
It's better to say, hey, I gave it my all, worked extremely hard but did not get a good grade -- this was a sign that maybe law wasn't meant for me. That's a much easier story to justify because science/medicine is an application in reasonable certainty whereas law is an application in advocacy/persuasion/writing so it's 2 entirely different skillset. Law is about oral argument, persuading others through reasoning and logic, thinking quick on your feet, public speaking, spinning the story that favors your client, being dynamic and charismatic in front of an audience (i.e. Obama). Medicine is not.
The other story just reeks, when the going got tough, I just gave up.