No, it's really not that significant, it was pretty expected. Before Obama, they never endorsed a Democrat for president, and they pretty much had to endorse Obama considering he was the Senator from Illinois. It's interesting to note that they did NOT endorse him when he was running for Senate in 2004, despite the fact that his opponent was just not good. This is a very typical move of the Tribune. And, they endorsed Rubio in the primary. Their endorsements have always had very strong, conservative leanings. It's significant only in that it's not Trump, but it's not representative of any ideological shift on their part, not really. It would have been at least surprising if not significant if they had endorsed Clinton because she's a Democrat. It's not something they would do. It would have been even more significant if they had endorsed no one. But endorsing Johnson, given how Chicago feels about Trump, was more expected than significant. This significance isn't necessarily a boost for 3rd parties, not directly, they are just saying 'Not Trump.' Edit: I have may have gotten that 2004 non-endorsement wrong ... I can't find who they endorsed and that was a very weird election as I recall now, with the Republican dropping out of the race in the final stretch, being replaced by Alan Keyes. However, their endorsements are more conservative than not, especially for top positions such as president and governor. I still think it was an unsurprising endorsement.