Air Carrier First Officer reported while landing at IAD; ATC allowed a helicopter to cross the runway resulting in an unsafe condition if a go-around was required.

Narrative

We were cleared to land 19L. I was the pilot flying. At around 700 feet above the ground the Tower called for us to see traffic; a helicopter that would be passing left to right. The helicopter was landing at an FBO.I did not see the traffic and I do not recall exactly when the Captain said he had a visual on the traffic.We were in a high workload environment and I was about to land. Shortly before crossing the threshold they called us two more times from the Tower to alert us of traffic.I did not have the traffic in sight and I wasn't even able to look because I was concentrating on the landing. About the time I started my power reduction over the threshold and was starting to do the flare; I glanced up and the helicopter was right over the middle of the runway; exactly where I would need to be if we did a go-around.What would have happened if we did a go around? It looked like a recipe for a midair collision. In hindsight; one of us (preferably the non flying pilot) should have said; 'traffic is NOT in sight;' but we were not given a lot of time to deal with the situation by ATC. Ideally; ATC would not have put us in a precarious situation on short final.Why could the helicopter not be told to remain east runway 19L until our landing was assured? It felt unnecessarily close and it felt like our go-around options were limited to only unsafe options due to the helicopter being given priority. Landing traffic; less maneuverable traffic; and lower altitude traffic should all have priority. I do not feel like this happened in this occurrence.