It seems to me the point is that mail-in ballots are often added later in election results. The RNC is reallocating their budget to legal challenges. This seems to anticipate two things:
the idea that mail-in ballots are corrupt will continue to be pushed. The “proof” will be how many more democrats there are in the mail-in ballots, partially due to the RNC attempting to minimize GOP mail-in ballots.
This will be informally reinforced by calls for armed Republicans to “stand watch” (aka voter intimidate) at ballot locations. This will disincentive in-person voting from democrats and increase the chances that mail-in ballots will seem partisan.
based on the actions of #2, on election day live votes will be tallied first, ideally showing a GOP win based on the idea the hope that more GOP will vote in person.
GOP will then immediately declare victory and try to delegitimize mail-in ballots as they begin to be counted and are “suspiciously” (intentionally) largely democratic ballots based on the consequences of #1.
Then they’ll try to sue to win by attempting to invalidate all mail-in ballots as “irregular,” which they will be, because the republican party will have attempted to make them irregular.