Only half of the delegates have already been voted on and Biden only has about 850 right now, so if Sanders were to remain in the race in any competitive way, both candidates would finish below the 1990 threshold and it would go to a contested convention. On the other hand, if Sanders were to stay in the race as an afterthought - where Biden continues to have all of the momentum (and thus gobble up most delegates) then he would in all likelihood reach 1990. The March 17th primaries are the last large batch of delegates up for grabs where Sanders could perform better than expected and create the perception that Biden's momentum is slowing down. Biden definitely has. the advantage at this point but stranger things have happened only as recently as 10 days ago when Biden came out of nowhere and surged into the lead.