When word broke that Bruce Rauner had won a ward in Chicago, some people were surprised, some people weren't, and some people wondered if it was a sign the city was getting more conservative.
In short? It's not surprising a Republican won a ward in Chicago. It's been done since 2000, in the far northwest-side 41st Ward, the most consistently Republican ward in the city. It's surprising that a Republican won the 42nd, which is reliably more Republican than the rest of the city, but not to the point of being a real stronghold.
But it's probably less surprising that Bruce Rauner was the Republican who won the 42nd, if that triangulates it for you. (We'll get back to triangulation in a minute.)
The 42nd Ward, like all wards and their boundaries, has changed shape over time. Fortunately, for my purposes, it hasn't changed shape that much (unlike, say, the 2nd). Generally speaking, it's the north part of the Loop, River North, and much of the Gold Coast. Comparing election returns there is less like comparing apples and oranges than it is different varieties of apples.
And its voting record is pretty consistent.
The 42nd has voted 2 to 2.5 times as Republican as the city as a whole for major candidates in recent elections; the only exception above is Alan Keyes, who was… an exceptionally bad choice. Bad candidates don't do well in the area just because they're Republicans—the obscure Sauerberg, the inexplicable Keyes, the unlucky (to draw a hometown hero) McCain couldn't break 30 percent.
That Rauner won the 42nd is probably not a sign that the ward, or Chicago, is getting more conservative; he was simply a very good choice if you happened to want to win that ward, which is likely a sign that Rauner did what he wanted to do—win over enough centrist/conservative, business-oriented Democrats to weaken Quinn. As Steve Bogira points out in the Reader, the 42nd is the city's wealthiest.
A useful comparison may be to the 2011 municipal election. The 42nd Ward was Rahm Emanuel's second-strongest ward, and only by one-tenth of a percent behind the neighboring 43rd Ward (encompassing Lincoln Park). If you round up to one decimal point, those are the only two wards where Emanuel broke 75 percent of the vote. And they were Rauner's two strongest wards. In the city's true Republican stronghold, the 41st, Emanuel lost by seven percentage points to Gery Chico—another centrist, business-friendly candidate, but without the burden of being one of the most powerful people in the Clinton and Obama administrations.