There seem to be three different groups:
1) Republican Senators who can see that Obamacare is actually about as right-wing a way to have universal healthcare as you can get**, and don't actually want to get rid of it.
2) Republican Senators who may or may not be in favour of Obamacare, but can see that their constituents are now attached to their healthcare, will be furious if they lose it, and only have a slim majority which they are terrified of losing at the next election.
3) Republican Senators who really are against Obamacare.
The problem here is that all three groups need to pretend that they're in category (3), because they've spent the last decade telling their supporters how terrible Obamacare is, to the point where there are voters who support all of the individual parts of the bill, and even the "Affordable Care Act" but will be will be against Obamacare.
And the longer the ACA exists, and the more that voters understand about it (as is happening the more Republicans talk about it) the more popular it gets. To the point where a majority of the public are now in favour of it***. But the Republican Party now has a central point of belief that "Obamacare is bad".
Which means that in order to be against it, but not actually remove it, we're left with a few Republican Senators taking it in turns to vote against repeal, on various largely spurious grounds. Being very careful to say "Oh no, I hate Obamacare as much as the next person. But I can't vote to repeal it this time, because of a minor provision. Maybe next time." - and then the next time a _different_ Republican Senator can do exactly the same thing.
None of which means that Obamacare is safe. It's balanced on a bunch of senators believing that if they repeal it they'll lose their jobs. So every time a repeal bill is put forward they have to be persuaded _again_ that the public still cares. And I am very grateful for my US friends who are involved in getting people to phone their representatives every time it comes up.
But I am moderately hopeful that we'll make it through to the mid-terms without it being repealed. Because I don't think that a majority of the senate actually wants it to be.****
*There were over 50 of these between 2011 and 2014, goodness knows how many we're up to now
**Not surprising, as it's very similar to RomneyCare.
***But only 17% of registered Republicans. It's the swing voters who have moved.
****But don't trust me. This is just my impression from what I've read from, frankly, a long way away.