After the Cubs won the NL pennant in 1945, the remnants of that team contended for a while the following year, as close as four games out of first place on July 20 before fading and finishing third, 13½ games behind the pennant-winning Cardinals.
And then... a whole bunch of nothing. The next five seasons were losing ones, including the team’s first-ever 90-loss season in 1948. They managed a .500 season in 1952, and were over .500 as late as Aug. 13, but far out of first place, 18½ games out.
Then 1953-58 were losing seasons again, three of them with 90+ losses (and that was harder in a 154-game season!