Arizona Congress Greg Stanton is a new Congressman. Here he attempts to grill Attorney General Bill Barr about the upcoming election. Stanton wants Barr to say he's going to make mail-in ballots count even if they are received after election day. Barr responds he will follow the law.
Each state passes their own laws regarding elections and mail-in ballots. Barr is simply saying he will follow those state passed laws.
On a side note. Here's how these hearings work. Each Democrat is assigned a role because these hearings are political reality TV. Stanton's role was to ask AG Barr about the elections to reinforce the conspiracy theory President Trump wouldn't leave the White House if he lost the November election.
Nothing but a show.