I don't think the backstop is the only problem with the Withdrawal Agreement but I do think resolving that issue will go a long way towards getting the Withdrawal Agreement passed.
I cannot understand the EUs position on this though.
As things stand we will leave on 29th March and there will be no backstop.
So surely a backstop with (say) a 6 month notice period would be better? That way if it looks like the UK and EU are not going to come to a settled agreement by 2023 the UK Govt of the day can give notice and there is time to deal with it.
Listening to Barnier today, as well as many MPs in the Commons currently, they are talking of the UK Government's red lines, but the backstop is a big red line of the EUs that is at the root of the problems with the WA.