"I'm wondering what people think should be done about US coastal cities as the seemingly inevitable global warming continues to melt polar ice and raise sea levels."

What did we do about it for last hundred years?

In next 50 years sea levels *will not* and unless something unforeseeable occurs *can not* rise more than than they did for last 100 hundred year. No one who has any understanding regarding this matter would dispute this. Gore [who doesn't qualify has having any understanding in this matter] would probably even agree with this. And people who claim that sea level will rise significantly, would not say that most of the sea level rise in next hundred years would be due to melting polar ice. But rather claim that most the rise would be due to the expansion of the ocean because the ocean is warming.
It's only when one is looking out over 500 to 1000 years does the possibility of melting polar ice become a *possible* concern.

Now as general rule coastal city on river deltas will lower, and could lower at a significantly faster rate than global or localized sea level rise. Without a city on the river delta [and water resource management] the land would generally rise, due to depositing of river sediment. As an example, if you were to allow New Orleans area to flood from seasonal and/or multiyear variation in river flow, river sediment would build up [and bury homes and other structures] and this in general would balance or exceed the land's sinking.

In other city coastal areas the land can be rising at a much faster rate than the global sea level rise. This due to the land "bouncing back" from crushing weigh of mile high glaciers which covered the continent, which geological speaking was very recent [about 10,000 year ago]. But this isn't consistent, some area are bouncing back at high rates, other area at slower rate or none at all. In some areas erosion is the most significant factor. And there are other factors.
The reason there is uncertainty about sea level rising [especially if you want measure in a short period of time- e.g. last couple of years] is that there many other factors which have a much larger effect than rising global sea level.
Btw, it's similar to measuring global temperature and both have a similar degree of an error bar as part of the measurement.