Remember, Pittsburgh has a 5:1 Democratic:Republican registration advantage even if the city does not produce consistent electoral results that are so lopsided. I no longer live in the city, instead I am about 200 yards east of the border and this is a futile strategy. Even accepting as a given a large pool of disenchanted liberal voters who are registered Democrats, even accepting the weakening of the Pittsburgh machine as evidenced by the defeat in Democratic primaries of two machine endorsed City Councilors and the felony indictment of another, the pool of voters who could potentially show up on election day AND flip is small.
Chris Briem at NullSpace is the go-to source for Pittsburgh electoral and economic data mapping and crunching and a couple of months ago he ran some numbers that are a good proxy for the strength of the Pittsburgh machine:
consider this as a benchmark: in November 2006, 40,899 voters in the city voted a straight Democratic Party ticket. So they didn't care about picking a non-Democrat in any race, they just pushed the Democrat button and that was that. This was out of 101,005 total votes cast in the city.... you start out being spotted 40 percentage points. It's worse than that in a sense. Those core party-line voters have a high probability of votingit is entirely possible that straight Democratic party voters will be a majority of all votes cast.
Then throw in voters like me who are Democratic partisans who voted a 90% Dem ticket in the 2003 local races (I voted against a couple of county row office incumbents as I believe them to be corrupt bastards) and it really does not matter in the short term. Luke Ravenstahl will win a truncated term and have a big fight in May of 2009 for the Democratic nomination for a full term.
So why talk about this lost cause case --- simply, it is an inverse example of the 50 state campaign objective that many liberal activists, myself included, and it is a good case study of what is achievable in very tough districts.
I think the coalition that Desantis needs to put together to win is an impossible coalition to form as I have a hard time seeing very liberal Bill Peduto supporters voting Republican on general principal despite a strong dislike of Ravenstahl, while at the same time, policies and pronouncements that could move disaffected liberals will alienate the GOP conservative base.
However, if DeSantis is able to run a campaign and assemble a coalition that is 50% larger than the typical Pittsburgh Republican coalition, which means winning slightly more than 40% of the vote instead of 27% of the vote, then he will have broken the Democratic stranglehold on Allegheny County with a potentially sustainable model. Right now that does not mean a whole lot, as the contested Congressional seats in this region (PA-4 Altmire (D-incumbent) and PA-18 T. Murhpy (R-incumbent) are non-Pittsburgh districts, but in 2012 after the redistricting, there is a decent chance of splitting Pittsburgh into two western PA districts as the region is losing population and the state will probably lose a seat.
If Desantis can run a proof of concept coalition expansion campaign than the Republican backers of his campaign will consider it a great success. In the same vein, Democrats who want to run a 50 state strategy will run plenty of our own Desantis's and fail in most cases, but occassionally expand the coalition and chip away at localized Republican institutional stregnth.