Traditional libertarians say that in general, people cannot be forced to provide for needy strangers, even if they could do so with relative ease. They do not (except for Ayn Rand, maybe) deny that we can have very strong obligations to provide assistance to certain people, but what they deny is the claim that we can generally be forced to provide such assistance, though it is owed. We have the right to do wrong, and that includes the right to withhold using our property to help people to whom duties of beneficence might be owed.
Rawlsians and other moderate left-liberals sometimes portray libertarians as being cruel or cold-hearted for this position. In their view, nice, humane political philosophies do not merely say that people ought to help, but that they ought to be forced to help. Or, alternatively, some Rawlsians might say that in certain instances, the property one withholds from the poor really belongs to the poor, not you, and so your refusal to help really amounts to a kind of stealing.
However, upon closer inspection, you might notice that Rawlsians say the same kind of thing as traditional libertarians, but simply draw the line a little differently. While libertarians say you generally cannot be forced to use your property to help strangers--even if you ought to help them--Rawlsians instead say that in a way, the production inside a single nation state belongs somewhat collectively to all the workers inside that nation state who produced it. They have enforceable obligations to ensure a certain kind of fair distribution of the value of that production among themselves, but not among others who did not contribute (according to the Rawlsians) to that production or among those who live outside the nation-state even if they did contribute. So, the orthodox Rawlsian view is that we the people cannot be forced to provide for needy strangers, even if we could do with relative ease, provided those needy strangers live on the opposite side of Trump's wall. Further, whether we can be forced to provide for needy strangers who live inside our national walls and fences is unclear, as it is unclear how much Rawls thinks we can be forced to provide for severely disabled people and others who cannot work.
In the end, rather than being so different, both views have the same position: You might owe things to the needy, but you can't be forced to provide for them. Even for Rawls, the reason some people get an enforceable claim to be fed and housed isn't the they are needy but that they sufficiently contributed to building the collective surplus.
UPDATE: As Chris Freiman comments, "They [Rawlsians] think people can be forced to provide air conditioning for the global 2% but not life saving help for someone living on 2 dollars a day."