Well, did the party force Fitzgerald out? Wasn't it his choice not to enter the primary even if the party wanted to put forth an "establishment" choice?
Fitz was never a part of the establishment. The anointed candidate in '96 was Loleta Didrickson, and after Fitz ate her lunch in the primary, she and the establishment went about badmouthing him to the point that he managed a too-narrow win over Carol Mostly-Fraud. When Fitz went about running a clean ship (in direct contrast to Gov. George Ryan's corrupt business-as-usual money train shakedowns) and promoted a crusading Fed Attorney (also named Fitzgerald, but no relation), these were unforgiveable sins to the state establishment. People like Fitz were way too dangerous because they'd bring a halt to corruption in both the state parties. The establishment GOP is as pleased as punch to allow anti-American kooks like Barack Hussein Obama to get into the Senate as long as he doesn't bother to do anything about the corruption. No different than the effortless shift of corruption in Chicago in the early '30s from the Republicans under Big Bill Thompson to the Democrats under Anton Cermak... same payoffs, different party, same end result... just business as usual.