On what grounds? The police, the coroner, the local prosecutors all closed it as an accident. Maybe Trump could have Barr open a federal investigation but the local authorities aren't going to. Not without new evidence.
In today’s politically correct World liberals can get cases reopened if they want.
For example in the Trayvon Martin case the police and local DA had closed the case based on the evidence they had that it was self-defense. But because of agitation by people like Al Sharpton the governor of Florida felt compelled to appoint a special prosecutor to look into the case.
It was the special prosecutor who brought murder charges against George Zimmerman not the local DA, who had already investigated the case and closed the case.
I don’t know enough about the details of Joe Scarborough situation. Just pointing out that the case could be reopened if powers-that-be wanted it reopened.
On the grounds that the investigation was compromised. Frankly at this point I don't trust law enforcement anymore.
Barr could use the reason he was a congressman at the time
On the grounds that the deep state coroner that “signed off” on it being an “accident” later had his licensed pulled and it was discovered he maintained a large collection of human body parts, etc.. ... or that Scarborough has never explained where he was that day because it makes no sense he would have made an appointment to meet with people the next morning at his office in FLA and never be there or that he’d have made the appointment to meet in FLA if he was in fact in DC as he’s since apparently maintained.