At this point, the GOP strategy to keep Trump in the White House is open to see. In 2016, he managed to get in by flipping three blue states: Michigan, Wisconsin and Pennsylvania. Right now, Biden is ahead in Michigan by 6.2. Wisconsin by 5.5 and Pennsylvania by 7.1 (RCP average). So they are all out of reach if the voters really decide.
The Republican plan is not to actually win the vote in any of these states, but rather to raise charges of electoral fraud, create chaos, get the Republican state congress to appoint Trump electors, litigate to the Supreme Court, and then have the Supreme Court somehow anoint Trump, as they did with W. Bush. They are pretty open about this, for example when Lindsey Graham says “Now, we may have litigation about who won the election, but the court will decide, and if the Republicans lose, we will accept that result.” They are already trying to plant the bizarre idea that the presidency will be decided by the Supreme Court rather than the vote.
So: how does one defend against this strategy? There are two main places to emphasize that differ from a normal election. One is countering the false accusations of fraud or electoral irregularity in MI, PA and WI. Especially in PA, which seems to be the preferred target for the litigation strategy.
But the other is to push hard in FL and AZ. A Biden win in either of those states makes the whole thing moot, and Biden is now ahead by 4.6 in Florida and 3.4 in Arizona. Of course, he could also pick up NC, GA, OH etc, where he holds small leads, but if that happens it is all over anyway.