The BBWAA rule to be able to vote for players for the HoF is a writer must have been an active baseball writer and BBWAA member for 10 years. As of 2015 another rule took effect—once you no longer actively/regularly covered baseball, the clock started ticking. After 10 years of not covering baseball, the writer loses his/her vote.
The first year of the voter purge, Barry Bonds and Roger Clemens saw their vote percentage jump from the mid thirties to the mid forties.
By 2016 the HoF instituted a new rule: players could no longer remain on the ballot for 15 years—henceforth the term of eligibility would be 10 years. They denied it was due to any particular players, but the math and logic are obvious.
The logic: older writers, the ones getting retired from eligibility to vote, are the ones who hate Bonds, Clemens, and other specific named alleged PED users. This was seen clearly in the percentage boost Bonds and Clemens received from the initial voter purge. The math? The new voters, ones less likely to use the HoF character clause as a bar to entry, were supporting the two at an 85% clip.
Last year Bonds and Clemens got 248 and 247 votes out of 400, respectively. Induction requires 75% of the vote. Their support has continued to increase a couple percentage points each year—just under 62% last year. That 2% comes from the new voters each year. Very few voters flip their votes on these two players each year. About 20 voters are culled each year and 20 added, with the total remaining about 400. That 85% support I mentioned earlier among new voters has also remained consistent.
This is now the 10th and final year on the ballot for Bonds and Clemens. They aren’t going to get to the necessary 75% for induction, even if a few voters who’ve withheld support previously vote for them now on their final chance. …but what if they still had five more years? Well they could count on around 85 more votes. Granted, they’d lose a few from retirees too—that’s why the increase each year has averaged around 2% and not over 3.5%. 5×2 = 10. Another 10% would get them to about 72% of the vote. At that range, a few final year flips could get them the needed 75% for HoF entry.
In short, it seems pretty obvious to me the shortening of the ballot eligibility period from 15 to 10 years was personal and intentional, not just coincidence. Next year Bonds and Clemens will be on the Today’s Game era (veterans committee) ballot, which so far has not been kind to Mark McGwire.