For all practical purposes, the brick and mortar beneath the Mookie Betts trade was laid the day Gerrit Cole agreed to a $324 million deal to be the ace of the New York Yankees, and the construction accelerated when the Boston Red Sox fired manager Alex Cora. Once Boston's primary rivals got the ace they needed, and once the Red Sox lost their most important staffer, the Red Sox situation gained clarity: It's going to be a year of turnover, the crossroad to the next big thing.
Without Cora, without Betts, Boston could still compete for a playoff spot in 2020, and if everything went right for the Red Sox and everything went wrong for the Yankees and Tampa Bay Rays, it's possible that the Sox could win the American League East. That latter scenario would require, for starters, many, many injuries manifesting in New York and Tampa Bay and Rafael Devers delivering an MVP performance.
But it's much more likely that this will be remembered as the year the Red Sox reset and took a turn back to consistent relevance, just as the Yankees did in 2016, when they traded Andrew Miller and Aroldis Chapman, extracted Gleyber Torres from the Cubs and introduced Aaron Judge to the big leagues.